Flange nuts
Integral bearing flanges, smooth and serrated faces, locking distinctions, and supplier-specific metric dimensions.
Tags: components, fasteners, nuts
On this page
Brighton-Best's metric serrated flange nut table lists M8 at 12.73–13 mm across flats, 7.6–8 mm height and 17.9 mm maximum flange diameter. The internal thread tolerance is 6H. The serrations follow its own design. Check the bearing face and the specified locking mechanism separately from the thread and wrench fit. BBI product data sheet, p. 1.
Identity and bearing face
An integral flange enlarges the bearing face of the nut. Bulten, Nuts.
The integral flange turns with the nut. A separate washer can remain stationary and has its own thickness, hardness and finish. Bulten, Nuts.
The underside and locking feature identify different variants:
| Feature | Meaning and limit |
|---|---|
| Smooth bearing face | A flange without bearing-face teeth; the flange alone does not identify a locking mechanism. |
| Serrated bearing face | Teeth engage the mating surface. Bossard illustrates penetration during tightening and shearing of surface material during loosening for BN 20230. Surface damage is part of that illustrated mechanism. |
| Prevailing torque feature | Resistance to rotation that exists independently of clamp load, rather than resistance arising only after the flange seats. |
The table combines terminology with engineering synthesis. The serration description is specific to Bossard BN 20230; the prevailing-torque definition comes from Nylok's glossary. Neither source proves universal resistance to vibration or loosening.
Thread, drive and mechanical designation
Hexagonal flange nuts have an external hexagon for wrench engagement. Thread diameter, pitch and fit describe the internal mating thread; width across flats describes the drive. They are different dimensions. Coarse and fine threads have separate reference families: ISO 4161:2012 covers style 2 coarse-thread flange nuts, M5–M20; ISO 10663:2012 covers style 2 fine-thread flange nuts with nominal diameters 8–20 mm. Both public abstracts specify product grade A through 16 mm and B above 16 mm. ISO 4161:2012, ISO 10663:2012
Material, mechanical class and surface finish are separate descriptors. For example, Bossard BN 20230 is steel, property class 8, zinc plated with thick-layer passivation; BN 14476 is listed as stainless steel A2. An A2 material label alone supplies no numeric mechanical class. Bossard BN 20230, Bossard BN 14476
Bulten separately lists steel classes 8, 10 and 12, stainless designations A2-70 and A2-80, and several coating processes across its nut range. These are examples of distinct designations, not options guaranteed for every flange nut. Engineering synthesis: neither the word “flange” nor a stainless group fixes proof strength, corrosion service, friction or tightening torque. Bulten, Nuts
Dimensional example and standards limits
Brighton-Best International's Serrated Hex Flange Nuts — Metric Series, marked Published 2026, gives the following dimensions in millimetres on page 1. The symbols are from that sheet's drawing. These are supplier-sheet examples, not a reproduction of a standards table. BBI product data sheet, p. 1
| Thread size | Across flats s, min–max (mm) |
Across corners e, min (mm) |
Height m, min–max (mm) |
Flange diameter dc, max (mm) |
|---|---|---|---|---|
| M8 | 12.73–13 | 14.38 | 7.6–8 | 17.9 |
| M10 | 14.73–15 | 16.64 | 9.6–10 | 21.8 |
BBI specifies internal thread tolerance 6H and states that serrations follow the manufacturer's design rather than DIN 6923. Its sheet calls DIN 6923 and ISO 4161 comparable and interchangeable; that supplier statement does not establish equivalence for every feature. BBI product data sheet, p. 1
Bossard marks DIN 6923 withdrawn. Its BN 20230 serrated listing uses approximate references ~DIN 6923 and ~ISO 4161, while BN 14476 lists DIN 6923 and EN 1661. Source comparison: these commercial cross-references are evidence of catalogue naming, not proof of identical dimensions, serrations or performance between standards. Bossard BN 20230, Bossard BN 14476
Flange versus prevailing torque
ISO identifies separate prevailing-torque flange-nut families: ISO 7043:2012 has a non-metallic insert; ISO 7044:2012 is all-metal. Their public abstracts both cover style 2 and M5–M20. These titles identify a locking construction in addition to the flange, rather than making every flanged nut a prevailing-torque nut. ISO 7043:2012, ISO 7044:2012
Nylok distinguishes running/prevailing torque from seating torque and from the torque needed to reverse a seated fastener. Engineering synthesis: an observed removal torque on a clamped serrated nut cannot by itself establish prevailing-torque performance. A washer interposed beneath serrations also changes the contact pair; performance demonstrated against the workpiece cannot automatically transfer to that assembly. Nylok glossary, Bossard BN 20230 functional principle
Applicability and source coverage
Engineering synthesis: fit and joint suitability depend jointly on the mating thread, nut height and wrench access, flange clearance, hole geometry, bearing material, surface finish, bolt/nut mechanical pairing and the specified tightening method. Flange diameter alone supplies neither effective contact area nor an allowable load. These sources do not establish structural qualification, a universal torque value, reuse life, vibration resistance or permission to omit a specified washer.
Sources were accessed October 30, 2026 PDT. ISO references above are limited to public catalogue abstracts and edition metadata: September 2012, third editions for 4161/7043/7044 and second edition for 10663, shown as confirmed in 2022. Full normative clauses and test requirements were not reviewed. The BBI drawing and dimensional table were visually inspected; its compilation disclaimer applies. Bossard, Bulten and Nylok pages carry no technical revision identifier in the cited content. Supplier listings establish their described products, not lot certification or customer-approved application limits.
Related reference: Hardware and component references.