{"id":14594,"date":"2026-10-29T14:45:37","date_gmt":"2026-10-29T06:45:37","guid":{"rendered":"https:\/\/sunhyings.com\/?p=14594"},"modified":"2026-10-29T14:45:37","modified_gmt":"2026-10-29T06:45:37","slug":"astm-a325-vs-a490-bolts-strength-coating-and-selection-differences","status":"publish","type":"post","link":"https:\/\/sunhyings.com\/it\/blog\/astm-a325-vs-a490-bolts-strength-coating-and-selection-differences\/","title":{"rendered":"Bulloni ASTM A325 e A490: differenze di resistenza, rivestimento e selezione"},"content":{"rendered":"\n<style>\n.sunhy-blog-article .sunhy-table-wrap{max-width:100%;overflow-x:auto;-webkit-overflow-scrolling:touch}\n.sunhy-blog-article .sunhy-table-wrap table{width:100%;border-collapse:collapse;min-width:680px}\n.sunhy-blog-article .sunhy-table-wrap th,.sunhy-blog-article .sunhy-table-wrap td{border:1px solid #d9dfe4;padding:0.7em 0.8em;text-align:left;vertical-align:top}\n.sunhy-blog-article .sunhy-table-wrap 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.sunhy-cta{background:#12354f;color:#f5f8fb;border:0}.sunhy-blog-article .sunhy-procurement-note a,.sunhy-blog-article .sunhy-cta a{color:#a9dffa}.sunhy-blog-article .sunhy-toc{background:#f7f9fb;border:1px solid #dce5ec;border-radius:10px;padding:22px 26px;margin:26px 0}.sunhy-blog-article .sunhy-toc-title{font-size:17px;color:#183f5d;margin:0 0 10px;font-weight:700}.sunhy-blog-article .sunhy-toc ol{margin:0;padding-inline-start:22px;columns:2;column-gap:30px}.sunhy-blog-article .sunhy-toc li{break-inside:avoid;margin:7px 0;line-height:1.5}\n.sunhy-blog-article .sunhy-table-wrap{width:100%;max-width:100%;overflow-x:auto;margin:25px 0;border:1px solid #d8e2eb;border-radius:9px;-webkit-overflow-scrolling:touch}.sunhy-blog-article .sunhy-table-wrap table{width:100%;min-width:640px;margin:0;border-collapse:collapse;font-size:15px}.sunhy-blog-article .sunhy-table-wrap th,.sunhy-blog-article .sunhy-table-wrap td{padding:14px 16px;vertical-align:top;line-height:1.6;border-bottom:1px solid #dce5eb}.sunhy-blog-article .sunhy-table-wrap thead th{background:#183f5c;color:#fff;text-align:start;font-weight:700}.sunhy-blog-article .sunhy-table-wrap tbody tr:nth-child(even){background:#f3f7fa}.sunhy-blog-article .sunhy-table-wrap tbody tr:last-child td{border-bottom:0}.sunhy-blog-article blockquote{background:#f3f7fa;border-inline-start:4px solid #849fb3;margin:24px 0;padding:20px 24px}.sunhy-blog-article blockquote p:last-child{margin:0}.sunhy-blog-article .sunhy-equation{padding:18px 22px;background:#eef4f8;border:1px solid #d6e3ec;border-radius:8px}\n.sunhy-blog-article .sunhy-editorial-figure{margin:30px 0}.sunhy-blog-article .sunhy-editorial-figure img{display:block;width:100%;height:auto;aspect-ratio:3\/2;object-fit:contain;background:#eaf0f4;border-radius:10px}.sunhy-blog-article .sunhy-editorial-figure figcaption{font-size:13px;line-height:1.65;color:#617685;padding:11px 3px}.sunhy-blog-article .sunhy-related-reading{background:#f4f8fb}.sunhy-blog-article .sunhy-related-reading ul{margin:0}.sunhy-blog-article .sunhy-reference-box{border-top:1px solid #dce5eb;background:#f8fafb;padding:22px;margin:32px 0;border-radius:8px;font-size:14px}.sunhy-blog-article .sunhy-reference-box h2{font-size:22px;background:none;border:0;padding:0;margin-top:0}\n@media(max-width:767px){.sunhy-blog-article{font-size:16px;line-height:1.75}.sunhy-blog-article h2{font-size:23px;margin-top:32px;padding:10px 13px}.sunhy-blog-article h3{font-size:19px}.sunhy-blog-article .sunhy-toc ol{columns:1}.sunhy-blog-article .sunhy-summary-box,.sunhy-blog-article .sunhy-warning-box,.sunhy-blog-article .sunhy-procurement-note,.sunhy-blog-article .sunhy-related-reading,.sunhy-blog-article .sunhy-cta,.sunhy-blog-article .sunhy-toc{padding:19px}.sunhy-blog-article .sunhy-table-wrap th,.sunhy-blog-article .sunhy-table-wrap td{padding:11px 13px}}\n\n.sunhy-blog-article .sunhy-faq details{border:1px solid #d4e1eb;border-radius:8px;background:#f7fafc;padding:17px 20px;margin:12px 0}.sunhy-blog-article .sunhy-faq summary{cursor:pointer;font-weight:700;color:#183f5c;line-height:1.5}.sunhy-blog-article .sunhy-faq details p{margin:14px 0 0}.sunhy-blog-article .sunhy-faq summary:focus-visible{outline:3px solid #bc842d;outline-offset:4px}\n<\/style>\n<article class=\"sunhy-blog-article\">\n<aside class=\"sunhy-summary-box sunhy-added\" aria-label=\"Quick answer\"><p class=\"sunhy-box-label\">Quick answer<\/p><p>ASTM A325 and A490 are both high-strength structural bolt grades, but <strong>A490 belongs to a higher tensile-strength group and has different coating restrictions<\/strong>. Under the 2025 RCSC Specification, ASTM F3125 Grade A325 is classified in Group 120, while Grade A490 belongs to Group 150. These designations correspond to nominal minimum tensile-strength levels of 120 ksi and 150 ksi, respectively.<\/p><\/aside><nav class=\"sunhy-toc sunhy-added\" aria-label=\"Article contents\"><p class=\"sunhy-toc-title\">In this guide<\/p><ol><li><a href=\"#a325-and-a490-under-astm-f3125-what-the-designations-mean\">A325 and A490 Under ASTM F3125: What the Designations Mean<\/a><\/li><li><a href=\"#strength-comparison-why-a-stronger-bolt-does-not-automatically-mean-a-stronger-joint\">Strength Comparison: Why a Stronger Bolt Does Not Automatically Mean a Stronger Joint<\/a><\/li><li><a href=\"#coating-differences-galvanizing-approved-coatings-and-corrosion-protection\">Coating Differences: Galvanizing, Approved Coatings and Corrosion Protection<\/a><\/li><li><a href=\"#when-should-engineers-specify-a325-or-a490\">When Should Engineers Specify A325 or A490?<\/a><\/li><li><a href=\"#how-to-specify-and-verify-a325-a490-bolt-assemblies\">How to Specify and Verify A325\/A490 Bolt Assemblies<\/a><\/li><li><a href=\"#sunhy-faq-14594\">Frequently asked questions<\/a><\/li><\/ol><\/nav>\n<p>That makes A490 the higher-strength product, but not automatically the better choice for a steel connection. The 25% difference between group designations does not translate into a blanket 25% increase in connection capacity. A325 and A490 must also be compared against the structural design, corrosion protection requirements, applicable installation provisions and compatible nuts and washers.<\/p>\n<aside class=\"sunhy-warning-box sunhy-added\" aria-label=\"Important specification check\"><p class=\"sunhy-box-label\">Important specification check<\/p><p>The coating distinction is especially important. Some galvanized assemblies that are acceptable with A325 cannot simply be replaced with A490 assemblies carrying the same coating. Conversely, saying that every zinc-based coating is prohibited on A490 is also incorrect under the 2025 RCSC rules.<\/p><\/aside>\n<h2 id=\"a325-and-a490-under-astm-f3125-what-the-designations-mean\">A325 and A490 Under ASTM F3125: What the Designations Mean<\/h2>\n<p>A325 and A490 were originally identified by separate ASTM specifications. Their structural bolting requirements are now addressed under <a href=\"https:\/\/store.astm.org\/f3125_f3125m-26.html\" target=\"_blank\" rel=\"noopener noreferrer nofollow\">ASTM F3125\/F3125M<\/a>, which consolidates several high-strength structural bolt product categories.<\/p>\n<p>In current specification language, an engineer may identify a bolt as ASTM F3125 Grade A325 or ASTM F3125 Grade A490. The grade identifies a specified mechanical strength category, while the type addresses material chemistry and related characteristics. These distinctions matter because a purchase order stating only \u201cA490 bolts\u201d may leave relevant material and coating details undefined.<\/p>\n<p>Both grades are associated with Type 1 and Type 3 material classifications where applicable. Type 1 represents the corresponding non-weathering material classification. Type 3 identifies a weathering-steel chemistry intended to improve atmospheric corrosion resistance under suitable exposure conditions. Type 3 is not a separate tensile-strength grade, and its designation does not mean that an applied protective coating is always unnecessary.<\/p>\n<p>Product style and dimensions are separate specification elements. A heavy-hex structural bolt must meet the dimensional requirements applicable to its specified product configuration; a visually similar standard hex bolt is not necessarily a compliant substitute. Nominal diameter, length, thread configuration and applicable product standard must be confirmed before the components are accepted as equivalent.<\/p>\n<p>The governing edition also matters. The ASTM publisher&#8217;s 2026 catalog identifies ASTM F3125\/F3125M-26, but a project may contractually require an earlier edition. An engineer or purchaser should not combine mechanical properties, coating permissions or acceptance procedures from different editions without establishing which requirements govern the order.<\/p>\n<p>ASTM F3125 addresses the bolt product; the installed structural joint must separately satisfy its governing design and installation requirements. For structural steelwork using the RCSC framework, those requirements include the relevant joint type, assembly, installation and inspection provisions.<\/p>\n<h2 id=\"strength-comparison-why-a-stronger-bolt-does-not-automatically-mean-a-stronger-joint\">Strength Comparison: Why a Stronger Bolt Does Not Automatically Mean a Stronger Joint<\/h2>\n<p>The principal mechanical difference is straightforward: A490 is assigned a higher minimum tensile-strength group than A325.<\/p>\n<p>The following comparison uses the 2025 RCSC bolting groups and coating provisions. It is not a reproduction of the full ASTM F3125 mechanical acceptance tables.<\/p>\n<div class=\"sunhy-table-wrap\" role=\"region\" aria-label=\"A325 and A490 structural bolt comparison\" tabindex=\"0\">\n<table>\n<thead><tr><th scope=\"col\">Characteristic<\/th><th scope=\"col\">Grade A325<\/th><th scope=\"col\">Grade A490<\/th><\/tr><\/thead>\n<tbody>\n<tr><td>ASTM product specification<\/td><td>ASTM F3125\/F3125M<\/td><td>ASTM F3125\/F3125M<\/td><\/tr>\n<tr><td>RCSC 2025 bolting group<\/td><td>Group 120<\/td><td>Group 150<\/td><\/tr>\n<tr><td>Group minimum tensile-strength level<\/td><td>120 ksi<\/td><td>150 ksi<\/td><\/tr>\n<tr><td>Relative tensile-strength grouping<\/td><td>Reference level<\/td><td>25% higher<\/td><\/tr>\n<tr><td>Hot-dip or mechanical galvanizing under RCSC 2025<\/td><td>Permitted for applicable compliant configurations<\/td><td>Prohibited for Group 150<\/td><\/tr>\n<tr><td>Zinc-flake coating<\/td><td>Eligibility and assembly requirements must be verified<\/td><td>Certain ASTM F3393 systems are conditionally permitted<\/td><\/tr>\n<tr><td>Structural joint capacity<\/td><td>Must be established by connection design<\/td><td>Must be established by connection design<\/td><\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n<p>The minimum tensile-strength grouping describes the bolt material requirement. It does not establish how much load an assembled connection can carry.<\/p>\n<p>Consider two bolts of the same nominal diameter, one A325 and the other A490. If their effective tensile areas are comparable, the higher-strength bolt offers greater potential resistance in a bolt-tension-controlled condition. That observation alone says nothing conclusive about the capacity of the complete connection.<\/p>\n<p>A steel connection may instead be governed by plate bearing, bolt-hole deformation, edge distance, connected-material strength, block shear or another applicable limit state. Increasing bolt material strength does not increase plate thickness, change edge distances or improve the strength of the surrounding connected material.<\/p>\n<p>The thread location also matters. Whether threads are included in a shear plane can influence the bolt shear resistance assigned by the governing design method. Simply changing the grade without reviewing the specified bolt geometry and connection details can leave an important design assumption unresolved.<\/p>\n<h3>Pretension is not the same as tensile strength<\/h3>\n<p>Another frequent source of confusion is the relationship between bolt tensile strength and installed pretension.<\/p>\n<p>Tensile strength is a material property established through the applicable product specification and testing requirements. Pretension is the clamping force developed in an installed bolt assembly when the connection requires pretensioning.<\/p>\n<p>For a slip-critical connection, resistance to slip depends on the applicable design relationship involving bolt pretension, the condition of the faying surfaces, the number of slip planes and other prescribed factors. A higher-strength bolt may permit a different specified pretension, but its effect on connection resistance must be evaluated using the governing design requirements.<\/p>\n<p>The bolt coating and the treatment of the faying surfaces are also distinct. Approval of a protective coating on the bolt does not establish that a particular coated or uncoated faying surface meets the required slip-resistance classification.<\/p>\n<p>In a bearing-type connection, the governing design checks can be different. Depending on the actual detail, increasing the bolt strength may offer an engineering benefit, provide no useful increase in the controlling connection resistance, or require other parts of the connection to be reconsidered.<\/p>\n<p><strong>The selection decision is therefore not \u201c150 ksi is better than 120 ksi.\u201d It is whether the higher-strength grade satisfies a documented structural requirement that the complete connection can make use of.<\/strong><\/p>\n<p class=\"sunhy-engineering-example sunhy-added\" data-example=\"1\">Consider an illustrative connection review where A490 is proposed to cure movement in an A325 joint. If the cause is an unverified installation procedure or unsuitable faying surfaces, a higher bolt grade does not resolve it. Identify the actual limit state and installation evidence before redesigning the connection. Use <a href=\"https:\/\/sunhyings.com\/blog\/understanding-bolt-grades\/\">bolt strength terminology<\/a> to keep product properties separate from joint performance.<\/p>\n\n<figure class=\"sunhy-editorial-figure sunhy-added\"><img loading=\"lazy\" src=\"https:\/\/sunhyings.com\/wp-content\/uploads\/2026\/10\/grade-8-zinc-plating-zinc-flake-coatings-sunhy.webp\" alt=\"Steel hex bolts with different zinc finishes on inspection bench\" width=\"1536\" height=\"1024\" loading=\"lazy\" decoding=\"async\" class=\"wp-image-14652\" title=\"A325 vs a490 structural bolts \u2014 illustrative inspection view\" srcset=\"https:\/\/sunhyings.com\/wp-content\/uploads\/2026\/10\/grade-8-zinc-plating-zinc-flake-coatings-sunhy.webp 1536w, https:\/\/sunhyings.com\/wp-content\/uploads\/2026\/10\/grade-8-zinc-plating-zinc-flake-coatings-sunhy-800x533.webp 800w, https:\/\/sunhyings.com\/wp-content\/uploads\/2026\/10\/grade-8-zinc-plating-zinc-flake-coatings-sunhy-1024x683.webp 1024w, https:\/\/sunhyings.com\/wp-content\/uploads\/2026\/10\/grade-8-zinc-plating-zinc-flake-coatings-sunhy-768x512.webp 768w, https:\/\/sunhyings.com\/wp-content\/uploads\/2026\/10\/grade-8-zinc-plating-zinc-flake-coatings-sunhy-18x12.webp 18w\" sizes=\"auto, (max-width: 1536px) 100vw, 1536px\" \/><figcaption>Steel hex bolts with different zinc finishes on inspection bench. Illustrative arrangement; appearance does not establish grade or product conformity.<\/figcaption><\/figure><h2 id=\"coating-differences-galvanizing-approved-coatings-and-corrosion-protection\">Coating Differences: Galvanizing, Approved Coatings and Corrosion Protection<\/h2>\n<p>Coating selection is one of the clearest practical differences between A325 and A490 structural bolts.<\/p>\n<p>Steel structural bolts may require corrosion protection when used outdoors, in industrial atmospheres or in other environments where unprotected steel is unsuitable. However, an acceptable coating must be evaluated as part of the specified bolt assembly. Its chemistry, application process, interaction with the fastener material and effect on installation can all matter.<\/p>\n<h3>Why hot-dip galvanizing and zinc-flake coatings must be distinguished<\/h3>\n<p>Hot-dip galvanizing and mechanical galvanizing are established zinc-coating processes, but their acceptance is not identical across the two structural bolting groups.<\/p>\n<p>Under the <a href=\"https:\/\/www.boltcouncil.org\/documents.html\" target=\"_blank\" rel=\"noopener noreferrer nofollow\">2025 RCSC Specification<\/a>, Group 150 bolting cannot be hot-dip galvanized or mechanically galvanized; specified ASTM F3393 zinc-flake systems are a separate, conditional route.<\/p>\n<p>This distinction prevents two opposite specification errors.<\/p>\n<p>The first error is ordering hot-dip galvanized A490 bolts because galvanized A325 bolts were previously accepted in a similar application. The higher-strength grade does not inherit the lower-strength group&#8217;s coating permissions.<\/p>\n<p>The second error is rejecting every zinc-based coating for A490. Certain ASTM F3393 zinc-flake coating systems are permitted within the applicable RCSC requirements. That permission is not a blanket approval for any commercial zinc-flake coating, arbitrary application process or unverified bolt-and-nut combination.<\/p>\n<p>The applicable coating specification, bolting grade, component configuration and qualification requirements must all agree.<\/p>\n<h3>Why high-strength bolt coatings receive special scrutiny<\/h3>\n<p>High-strength steel fasteners can be susceptible to hydrogen-assisted cracking under unfavorable combinations of material condition, applied stress and hydrogen exposure.<\/p>\n<p>Coating and surface-treatment processes may introduce or influence that risk. Its significance depends on the strength and material characteristics of the fastener and the specific processing route.<\/p>\n<p>This is one reason coating suitability cannot be judged solely by the appearance or nominal corrosion resistance of the finished bolt. A process that produces acceptable corrosion protection does not necessarily satisfy the requirements applicable to a particular high-strength structural bolt grade.<\/p>\n<p>Measures intended to control hydrogen-related risks also do not override explicit prohibitions in the governing structural bolting specification.<\/p>\n<p>There is an additional assembly consequence. Protective coatings can alter thread dimensions and frictional behavior. Galvanized or otherwise coated fasteners may require specific matching nut conditions and lubrication provisions. Combining a coated bolt with an unrelated nut is not equivalent to procuring a compliant structural bolting assembly.<\/p>\n<p>When pretensioning is required, the specified assembly and installation procedure must also be capable of satisfying the applicable verification requirements. Coating qualification, product testing and field installation verification are related but separate responsibilities.<\/p>\n<h3>Type 3 weathering steel is another selection route<\/h3>\n<p>Type 3 structural bolts use weathering-steel material characteristics rather than relying exclusively on a subsequently applied protective coating.<\/p>\n<p>In suitable atmospheric exposure, weathering steels can develop a protective corrosion-product layer that reduces further atmospheric corrosion compared with conventional unprotected steel. Their effectiveness depends on the environment and the conditions that allow the protective layer to develop.<\/p>\n<p>Persistent wetness, aggressive chloride exposure, contaminated runoff and sheltered moisture-retaining details can change that behavior. A weathering designation alone does not establish acceptable corrosion performance in every outdoor location.<\/p>\n<p>Where Type 3 bolts are specified, matching nuts and washers must also satisfy the applicable assembly requirements. Combining weathering and non-weathering components without checking the specified configuration can create an unintended materials mismatch.<\/p>\n<p>The real decision is between approved protection systems for the actual service environment, not between a supposedly corrosion-proof bolt and one that always needs coating.<\/p>\n<p class=\"sunhy-engineering-example sunhy-added\" data-example=\"2\">In a hypothetical outdoor order, the buyer changes A325 to A490 while retaining the hot-dip-galvanized finish line. The original coating permission cannot be carried across automatically. Hold the revised order, check the permitted coating route and confirm the corresponding nuts, washers and assembly evidence. Compare coating processes without treating a finish name as structural approval.<\/p>\n\n<h2 id=\"when-should-engineers-specify-a325-or-a490\">When Should Engineers Specify A325 or A490?<\/h2>\n<p>A325 is a reasonable selection when the governing structural design permits Group 120 bolting and its available, compliant corrosion-protection options satisfy the project requirements.<\/p>\n<p>A490 becomes relevant when the engineer specifies Group 150 bolting or establishes that the higher-strength product offers a useful advantage for the actual connection design. That decision must still account for coating restrictions, assembly requirements and installation conditions.<\/p>\n<p>The comparison becomes more useful when applied to specific purchasing situations.<\/p>\n<p><strong>A connection already designed and approved for A325<\/strong><\/p>\n<p>If an approved connection specifies Grade A325, purchasing should follow that designation unless a formal substitution is accepted. A490 should not be treated as an automatic upgrade merely because it has a higher minimum tensile-strength level.<\/p>\n<p>Changing the grade may alter design assumptions, pretension requirements, coating eligibility and matching component selection. Even when the proposed bolt has the same nominal diameter and thread, those differences require review.<\/p>\n<p><strong>A connection where higher-strength bolting is specified<\/strong><\/p>\n<p>If the structural design specifically requires Grade A490, substituting A325 because it is more readily available or easier to galvanize is not acceptable without an engineering review.<\/p>\n<p>The lower-strength grade may not satisfy the design basis. Where corrosion protection is also required, the coating system must be compatible with the specified higher-strength bolting group rather than selected independently.<\/p>\n<p><strong>An outdoor connection requiring corrosion protection<\/strong><\/p>\n<p>For an outdoor structural assembly, the designer must establish whether an appropriately galvanized Group 120 assembly, an approved coated Group 150 assembly or a suitable weathering-steel configuration fulfills the combined structural and exposure requirements.<\/p>\n<p>The environmental requirement cannot be separated from the mechanical requirement. A coating acceptable on one grade is not necessarily transferable to the other, while a weathering material may be unsuitable for particular wet or chloride-rich conditions.<\/p>\n<h3>Hypothetical selection example: a proposed bolt upgrade<\/h3>\n<p>Consider a hypothetical outdoor steel connection whose approved documents specify ASTM F3125 Grade A325 Type 1 bolts with a compliant hot-dip galvanized assembly.<\/p>\n<p>A purchaser proposes replacing the specified bolts with Grade A490 of the same nominal diameter, also hot-dip galvanized, on the assumption that stronger bolts provide a greater safety margin.<\/p>\n<p>That substitution has two separate problems.<\/p>\n<p>First, the stronger bolt does not automatically increase the approved connection resistance. The design would need to be checked against the relevant limit states and installation assumptions.<\/p>\n<p>Second, the proposed hot-dip galvanized Group 150 configuration conflicts with the 2025 RCSC coating restriction. Matching the original bolt diameter cannot resolve a coating prohibition.<\/p>\n<p>The appropriate response is to retain the specified compliant A325 assembly unless the engineer approves a different design and matching bolting configuration. If A490 is genuinely required, the protection system must be selected from the options permitted by the governing project requirements, with any applicable ASTM F3393 qualification independently confirmed.<\/p>\n<p>This is an illustrative engineering scenario, not a SUNHY customer project, test result or approval of a particular product.<\/p>\n<h2 id=\"how-to-specify-and-verify-a325-a490-bolt-assemblies\">How to Specify and Verify A325\/A490 Bolt Assemblies<\/h2>\n<p>A <a href=\"https:\/\/sunhyings.com\/fasteners\/bolts\/structural-bolts\/\">structural bolt<\/a> order should identify more than the grade printed on the drawing.<\/p>\n<p>The buyer needs sufficient information to distinguish the specified bolt product from visually similar fasteners, confirm the correct corrosion-protection system and ensure that the matching components meet the project requirements.<\/p>\n<p>A practical purchasing specification should establish the following:<\/p>\n<ol>\n<li><strong>Product identity:<\/strong> ASTM F3125\/F3125M, the governing edition, Grade A325 or A490, applicable Type, product style, nominal diameter, length and thread configuration.<\/li>\n<li><strong>Coating and exposure:<\/strong> Required surface protection, the exact coating specification, its eligibility for the selected grade and the relevant corrosion environment.<\/li>\n<li><strong>Matching components:<\/strong> Applicable nut and washer product specifications, their grades or types, coating compatibility and any specified lubrication or assembly conditions.<\/li>\n<li><strong>Joint requirements:<\/strong> The approved structural design basis, whether pretensioning is required, applicable installation method and any project-specific inspection requirements.<\/li>\n<li><strong>Acceptance documents:<\/strong> Manufacturer identification, product and lot traceability, required material or mechanical test records, coating documentation and any additional project inspection evidence.<\/li>\n<\/ol>\n<p>ASTM A563 nuts and ASTM F436 washers are commonly referenced in structural bolting assemblies, but their acceptable grades, types and coating combinations depend on the applicable specifications. A purchaser should not select a nut solely by nominal thread size or assume that any hardened washer satisfies every structural connection requirement.<\/p>\n<p>The same principle applies to testing and documentation. A manufacturer may provide test records showing that a production lot was evaluated against specified product requirements. Those records do not by themselves demonstrate that a field-installed joint achieved the required pretension or that its installation inspection was completed correctly.<\/p>\n<p>Product qualification and joint acceptance therefore require different evidence.<\/p>\n<p>Bolt head markings can help identify the declared grade and manufacturer, but visual markings alone do not establish material chemistry, tensile-test compliance, coating qualification or full lot traceability. Receiving inspection should reconcile the actual components with the purchase order, applicable standard and supplied documentation.<\/p>\n<p>For pretensioned assemblies, preinstallation verification and installation inspection must follow the governing requirements. A generic torque chart is not an adequate substitute for those procedures, since the torque needed to develop a particular clamp load can vary with the fastener assembly and its frictional condition.<\/p>\n<p>There is also a difference between a supplier offering a nominally matching bolt and supplying a documented assembly acceptable for the specified structural work. If the requested grade, coating or matching components cannot be supported by appropriate records, the discrepancy should be resolved before substitution or installation.<\/p>\n<aside class=\"sunhy-procurement-note sunhy-added\"><p>When <a href=\"https:\/\/sunhyings.com\/contact-us\/\">requesting a quotation<\/a> for A325 or A490 structural bolt assemblies, provide the governing specification and edition, complete bolt dimensions, Grade and Type, required finish, assembly configuration, quantity and documentation requirements. Ask the supplier to confirm the exact available configuration and supporting evidence rather than assuming that every coating or companion component is interchangeable.<\/p><\/aside>\n<p>The final choice should preserve the engineer&#8217;s approved connection requirements. Material strength determines only part of what a structural bolt can do; coating eligibility, matched components and verified installation requirements determine whether that bolt can be used as specified.<\/p>\n<aside class=\"sunhy-related-reading sunhy-added\" aria-label=\"Related technical reading\"><p class=\"sunhy-box-label\">Related technical reading<\/p><ul><li><a href=\"https:\/\/sunhyings.com\/fasteners\/bolts\/structural-bolts\/\">Structural bolt specification and enquiry<\/a><\/li><li><a href=\"https:\/\/sunhyings.com\/blog\/hex-nut-grades-explained\/\">Hex nut grades and selection checks<\/a><\/li><li><a href=\"https:\/\/sunhyings.com\/blog\/hydrogen-embrittlement-risk-high-strength-coated-nuts\/\">Hydrogen-embrittlement controls for high-strength fasteners<\/a><\/li><li><a href=\"https:\/\/sunhyings.com\/blog\/traceability-for-automotive-fasteners\/\">Fastener lot control and inspection-record principles<\/a><\/li><\/ul><\/aside>\n<section class=\"sunhy-faq sunhy-added\" aria-labelledby=\"sunhy-faq-14594\"><h2 id=\"sunhy-faq-14594\">Frequently asked questions<\/h2><details><summary>Is A490 always the better structural bolt?<\/summary><p>No. The correct grade follows the approved connection design, installation and corrosion-protection requirements. A higher tensile-strength group does not automatically improve every joint.<\/p><\/details><details><summary>Can A490 bolts be hot-dip galvanized under RCSC 2025?<\/summary><p>No. The cited specification prohibits that route for Group 150 bolts. Other qualifying coating routes have separate conditions and must be checked.<\/p><\/details><details><summary>Can I reuse the A325 nut specification after changing to A490?<\/summary><p>Check it again. Permitted nut grades depend on bolt Group, Type and coating condition; matching nominal thread size is insufficient.<\/p><\/details><\/section>\n<\/article>\n<script type=\"application\/ld+json\">{\"@context\": \"https:\/\/schema.org\", \"@type\": \"FAQPage\", \"@id\": \"https:\/\/sunhyings.com\/blog\/astm-a325-vs-a490-bolts-strength-coating-and-selection-differences\/#faq\", \"mainEntity\": [{\"@type\": \"Question\", \"name\": \"Is A490 always the better structural bolt?\", \"acceptedAnswer\": {\"@type\": \"Answer\", \"text\": \"No. The correct grade follows the approved connection design, installation and corrosion-protection requirements. A higher tensile-strength group does not automatically improve every joint.\"}}, {\"@type\": \"Question\", \"name\": \"Can A490 bolts be hot-dip galvanized under RCSC 2025?\", \"acceptedAnswer\": {\"@type\": \"Answer\", \"text\": \"No. The cited specification prohibits that route for Group 150 bolts. Other qualifying coating routes have separate conditions and must be checked.\"}}, {\"@type\": \"Question\", \"name\": \"Can I reuse the A325 nut specification after changing to A490?\", \"acceptedAnswer\": {\"@type\": \"Answer\", \"text\": \"Check it again. Permitted nut grades depend on bolt Group, Type and coating condition; matching nominal thread size is insufficient.\"}}]}<\/script>\n","protected":false},"excerpt":{"rendered":"<p>Confronta i gruppi di resistenza dei bulloni ASTM A325 e A490, i limiti della zincatura a caldo, i rivestimenti qualificati a scaglie di zinco e ci\u00f2 che i tecnici devono verificare prima della specifica.<\/p>","protected":false},"author":1,"featured_media":14625,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[35],"tags":[],"class_list":["post-14594","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-selection-comparison"],"_links":{"self":[{"href":"https:\/\/sunhyings.com\/it\/wp-json\/wp\/v2\/posts\/14594","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/sunhyings.com\/it\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/sunhyings.com\/it\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/sunhyings.com\/it\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/sunhyings.com\/it\/wp-json\/wp\/v2\/comments?post=14594"}],"version-history":[{"count":2,"href":"https:\/\/sunhyings.com\/it\/wp-json\/wp\/v2\/posts\/14594\/revisions"}],"predecessor-version":[{"id":14692,"href":"https:\/\/sunhyings.com\/it\/wp-json\/wp\/v2\/posts\/14594\/revisions\/14692"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/sunhyings.com\/it\/wp-json\/wp\/v2\/media\/14625"}],"wp:attachment":[{"href":"https:\/\/sunhyings.com\/it\/wp-json\/wp\/v2\/media?parent=14594"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/sunhyings.com\/it\/wp-json\/wp\/v2\/categories?post=14594"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/sunhyings.com\/it\/wp-json\/wp\/v2\/tags?post=14594"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}