Hex Flange Nuts (Serrated, Smooth & Nylon Insert Flange Nuts)
When a joint fails in the field, the root cause is often not “insufficient strength” but loss of clamp load: embedding on soft bearing surfaces, vibration-induced micro-slip, or inconsistent friction from stacked washers. Hex flange nuts address these realities with an integrated flange that increases bearing area and improves load distribution—removing the variability of separate washers.
In high-throughput production lines (automotive brackets, chassis sub-assemblies, solar racking, agricultural equipment), the choice is rarely one-size-fits-all: serrated flange nuts (whiz nuts) are used when anti-rotation bite is required; smooth flange nuts are chosen when the mating surface must remain intact; and nylon insert flange nuts add prevailing torque for vibration resistance where a polymer insert is acceptable. The image reflects these three functional variants, commonly supplied in zinc-plated carbon steel and stainless steel programmes.
- Integrate washer-bearing flange
- Reduce embedment preload loss
- Offer serrated anti-rotation teeth
- Provide smooth, non-marring flange
- Supply nylon insert flange options
- Support DIN/ISO/JIS compliance
Technical Specifications
Product Name
Hex Flange Nuts / Flange Nuts / Flanged Hexagon Nuts / Hex Nuts with Flange / Collar Nuts / Washer Nuts
Standards
DIN 6923 / ISO 4161 (hex flange nuts, serrated or non-serrated by type), DIN 6926 (nylon insert flange lock nuts), IFI 100/107 (inch flange nut programmes), JIS B 1190 (JIS flange nuts)
Material
Carbon steel, Alloy steel; Stainless steel A2 (304) / A4 (316)
Grades / Classes
Metric programmes: common Class 8 / Class 10 (as specified); Stainless: A2-70 / A4-70 / A4-80 where required
Thread
Metric coarse/fine; UNC / UNF on request
Diameter Range
Metric: common M4–M24 (larger by request); Inch sizes per IFI programmes
Surface Finish
Zinc plated (blue/white), Yellow zinc plated (yellow chromate), plain; Stainless passivated; Zinc-nickel / flake coatings available for corrosion + friction control
Certifications
ISO 9001:2015, RoHS/REACH declarations on request, EN 10204 3.1 MTC and lot traceability available
1: Preload loss from embedding and washer stacking
What happens: Separate washers can settle or “bed in,” causing early preload drop after tightening. Surface coatings can also compress under load.
Flange nut solution: The flange increases bearing area and distributes contact pressure, reducing local embedment—especially useful on mild steel brackets and thin-gauge parts.
2: Vibration loosening (need anti-rotation at the bearing face)
Serrated flange nuts (DIN 6923 / ISO 4161 serrated type): Serrations create a mechanical bite into the mating surface, raising resistance to rotation.
Practical note: Serrations can mark coatings or soft materials; specify “serrated” only when surface damage is acceptable and joint retention is prioritised.
3: Surface protection and torque consistency
Smooth flange nuts (non-serrated): Preferred when the bearing surface is painted, anodised, stainless, or cosmetic, and serration marking is not allowed.
Engineering trade-off: Smooth flange relies more on clamp load and friction; if vibration is severe, combine with a prevailing torque feature or validated washer solution.
4: “Dual-locking” demand in compact assemblies
Nylon insert flange nuts (DIN 6926): Add prevailing torque via nylon insert while keeping the flange for load distribution.
Limitations: Nylon inserts are temperature- and chemical-sensitive; for hot zones (exhaust proximity, high ambient), consider all-metal locking strategies instead.
Example “metric flange nut dimensions” table for SEO intent. Confirm exact dimensions and tolerances against the specified standard edition.
| Thread d | Pitch P (coarse) | Across flats s | Nut height m | Flange diameter dc |
|---|---|---|---|---|
| M6 | 1.0 | 10 | 6 | 14.2 |
| M8 | 1.25 | 13 | 8 | 17.9 |
| M10 | 1.5 | 15 | 10 | 21.8 |
| M12 | 1.75 | 18 | 12 | 26.0 |
| M16 | 2.0 | 24 | 16 | 33.8 |
| M20 | 2.5 | 30 | 20 | 42.8 |
Dimension checks that prevent fit issues
Verify dc fits the seating land (avoid flange overhang).
Ensure m provides required thread engagement (especially on short studs).
For serrated types, validate that the bearing face is suitable for tooth bite.
Torque & preload: control friction, don’t guess
Flange nuts reduce washer-related variability, but torque scatter still comes from thread/bearing friction and coatings. If your programme is sensitive, specify lubrication condition and verify torque–tension correlation.
Serrated vs smooth: match to the bearing surface
Serrated flange nuts: Use on steel surfaces where marking is acceptable; avoid on aluminium, soft alloys, painted/anodised parts, or thin coatings where teeth may damage and relax the joint.
Smooth flange nuts: Use where surface protection is needed; for vibration, consider nylon insert flange nuts (DIN 6926) or other locking measures.
Washers: when they still matter
In very soft materials or slotted holes, a hardened washer can still be justified to prevent galling or embedment—even with a flange—provided the stack-up is validated.
Hole clearance (ISO 273)
Clearance holes must follow ISO 273 to prevent joint binding. Binding creates “false torque” (high torque, low preload), which defeats both serrations and prevailing torque features.
Service temperature check (for nylon insert flange nuts)
If the joint sees elevated temperature or chemical exposure, do not assume nylon retention. For hot zones, move to all-metal locking solutions or validated mechanical locking.
Related Products
FAQ
What is a hex flange nut used for?
A hex flange nut is used to distribute load and improve joint stability by integrating a washer-like flange under the nut. It reduces bearing stress and can reduce preload loss from embedment compared with a standard hex nut plus washer stack.
What is a serrated flange nut (whiz nut)?
A serrated flange nut is a flange nut with teeth on the bearing face that bite into the mating surface to resist rotation. It is commonly selected for anti-loosening in vibration environments where surface marking is acceptable.
What is the difference between DIN 6923 and DIN 6926?
DIN 6923 covers hex flange nuts (serrated or non-serrated types depending on design), while DIN 6926 covers nylon insert flange lock nuts that add prevailing torque via a nylon insert for vibration resistance.
Should I use serrated flange nuts on aluminium or painted surfaces?
Generally no—serrations can damage aluminium or painted/anodised surfaces and may reduce long-term clamp consistency. For protected or soft surfaces, use smooth flange nuts or a nylon insert flange nut if temperature allows.
Do flange nuts eliminate the need for washers?
Often yes, because the flange provides a larger bearing area, but not always. In slotted holes, very soft materials, or where surface protection is critical, a washer may still be required after joint validation.