Button Head Socket Screws (BHCS)
In compact assemblies, a protruding head becomes a mechanical problem: it catches cables, interferes with sliding parts, or violates envelope clearance. A Button Head Socket Screw solves this with a low-profile, rounded head while keeping torque transmission inside the head via a hex socket—useful where a spanner cannot be applied and external hex heads would foul nearby geometry.
Where projects fail is usually not “strength”—it’s socket strip, preload loss from embedment on soft substrates, or fretting under micro-motion when the joint sees vibration. For these scenarios, we supply both ISO 7380-1 (standard button head) and ISO 7380-2 (button head with collar) so engineers can choose between compact head height and increased under-head bearing area—without changing the drive system.
- Reduce head height; save clearance
- Maintain torque via hex socket
- Offer collar version; spread load
- Support Class 10.9 / 12.9
- Provide A2-70 / A4-80
- Control finish; stabilise friction
Technical Specifications
Product Name
Button Head Socket Screws / Button Head Socket Cap Screws (BHCS)
Standards
ISO 7380-1 (button head, hex socket), ISO 7380-2 (button head with collar), ASME B18.3 (inch series, button head socket)
Material
Alloy steel (e.g., SCM435 / 42CrMo / 4140 Q&T), Carbon steel (project-dependent), Stainless steel A2 (304) / A4 (316)
Grades
Metric steel: 10.9 / 12.9 (per ISO 898-1); Stainless: A2-70 / A4-70 / A4-80 (per ISO 3506, when specified)
Diameter Range
Typical metric: M3–M16 (other sizes on request); inch sizes per ASME B18.3 on request
Surface Finish
Black oxide, Zinc plated (Cr3), Zinc-Nickel, Geomet/Dacromet (flake coating), Phosphate & oil, Passivation (stainless)
Certifications
ISO 9001:2015, EN 10204 3.1 MTC, RoHS/REACH declarations on request; PPAP/traceability options for OEM programs
1: Head interference and snagging in tight envelopes.
What happens in real assemblies: Cable management, guarding panels, and sliding mechanisms fail clearance checks because a hex head or pan head protrudes too far.
How BHCS helps: The rounded, low-profile head reduces snag risk and improves clearance without requiring a countersink operation.
2: Embedment and preload decay on soft substrates.
What happens in service: On aluminium brackets, coated sheet metal, or plastics, under-head contact stress causes local crushing (embedment). Clamp load drops, and vibration accelerates micro-slip.
Solution choice:
ISO 7380-2 (with collar): increases bearing area to reduce contact pressure and slow embedment-driven preload loss.
ISO 7380-1 (standard): preferred when OD constraints are tight or when collar interference exists.
3: Socket stripping during assembly or rework.
What happens on the line: Tool wear, misalignment, or ball-end keys under torque round the socket, turning a simple service task into drilling/extraction.
Engineering response: specify appropriate property class (10.9/12.9 where clamp load is critical), control surface finish/lubrication, and enforce driver engagement rules in work instructions.
4: Corrosion at the head interface and galvanic pairing.
What happens outdoors: Moisture traps under the head; coating damage during tightening becomes an initiation site. Stainless-to-aluminium pairs may raise galvanic concerns depending on environment.
Solution: select finish (zinc-nickel or flake coatings) or A4/316 for chloride exposure, and manage lubrication to reduce galling (stainless).
Example dimensions for “Button Head Socket Screw dimensions” searches. Confirm the exact standard edition and tolerance requirements for release.
| Thread d | Pitch P (coarse) | Hex socket s | Head Ø dk (typ.) | Head height k (typ.) | Thread length b |
|---|---|---|---|---|---|
| M3 | 0.5 | 2.0 | 5.7 | 1.65 | ≈ L (full thread) |
| M4 | 0.7 | 2.5 | 7.6 | 2.20 | ≈ L (full thread) |
| M5 | 0.8 | 3.0 | 9.5 | 2.75 | ≈ L (full thread) |
| M6 | 1.0 | 4.0 | 10.5 | 3.30 | ≈ L (full thread) |
| M8 | 1.25 | 5.0 | 14.0 | 4.40 | ≈ L (full thread) |
| M10 | 1.5 | 6.0 | 17.5 | 5.50 | ≈ L (full thread) |
If you need higher bearing area
ISO 7380-2 adds a collar (flange) under the head. In drawings and procurement, call out “-2” explicitly to avoid mixing collar and non-collar parts in the same line build.
Achieve target preload with repeatable torque transfer and without socket damage.
Hole Clearance (ISO 273)
For through-holes, use ISO 273 close/normal/large clearance series per your alignment tolerance and process capability.
Too-tight clearance increases binding and false torque; too-large clearance can increase joint slip risk under transverse loading.
Torque, Preload, Lubrication
Torque is friction-dominated. Define the assembly condition (dry vs oiled vs coated) and keep it consistent across suppliers.
Practical relationship: T = K × F × d (K varies with finish/lube).
Indicative K ranges: dry 0.18–0.25, light oil 0.14–0.20, anti-seize 0.10–0.16.
For critical joints, validate with torque–tension testing (e.g., ISO 16047 methodology) and lock down the friction window.
Driver engagement rules (prevents socket strip)
Use the correct hex key size; ensure full depth engagement before applying torque.
Avoid ball-end keys for final torque. Replace worn drivers early—most rounded sockets start with tool wear.
Washer strategy
Standard BHCS often seats directly on the surface.
Use washers when:
substrate is soft (aluminium/plastic) and embedment is a concern
slot holes or oversize holes are present
you need electrical isolation or controlled bearing surface
For flange-bearing needs, consider ISO 7380-2 (collar) as an alternative to adding washers.
Stainless galling control
For A2/A4 screws, galling risk increases with high clamp loads and dry assembly. Specify compatible nuts/inserts where relevant and apply appropriate lubrication/anti-seize per your corrosion policy.
Related Products
FAQ
What is a button head socket screw used for?
Button head socket screws are used where low head height and internal-hex tightening are needed in tight-clearance assemblies. They reduce snagging and interference compared with external-hex heads.
What is the difference between ISO 7380-1 and ISO 7380-2?
ISO 7380-1 is the standard button head design, while ISO 7380-2 includes a collar (flange) under the head. The collar increases bearing area and helps reduce embedment and preload loss on softer materials.
Are button head socket screws as strong as socket head cap screws?
Tensile strength depends on the property class (e.g., 10.9 or 12.9), not the head shape. However, socket head cap screws (ISO 4762) typically have a more robust head/drive for higher tightening torque and repeated rework.
Why does the hex socket strip out during tightening?
Socket stripping is usually caused by poor driver engagement, wrong key size, tool wear, or excessive torque—often made worse by inconsistent lubrication/friction. Full engagement and controlled assembly conditions are the primary fixes.
Can you supply button head socket screws in stainless steel?
Yes—common options include A2-70 (304) and A4-70/A4-80 (316). Stainless is selected for corrosion resistance, but installation should manage galling risk via lubrication and compatible mating components.