# Flange nuts

Integral bearing flanges, smooth and serrated faces, locking distinctions, and supplier-specific metric dimensions.

Reviewed: 2026-10-30

Tags: components, fasteners, nuts

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](https://www.brightonbest.com/download/pds/PDS_Metric_Serrated_Hex_Flange_Nuts.pdf).

## Identity and bearing face

An integral flange enlarges the bearing face of the nut. [Bulten, Nuts](https://www.bulten.com/en/products/nuts/).

The integral flange turns with the nut. A separate washer can remain stationary and has its own thickness, hardness and finish. [Bulten, Nuts](https://www.bulten.com/en/products/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](https://www.bossard.com/global-en/eshop/metallic-locking-nut/hex-nuts-with-flange-and-serrations/p/20230/); the prevailing-torque definition comes from [Nylok's glossary](https://nylok.com/our-resources/fastener-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](https://www.iso.org/standard/61523.html), [ISO 10663:2012](https://www.iso.org/standard/61527.html)

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](https://www.bossard.com/global-en/eshop/metallic-locking-nut/hex-nuts-with-flange-and-serrations/p/20230/), [Bossard BN 14476](https://www.bossard.com/global-en/eshop/hex-nuts/hex-flange-nuts/p/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](https://www.bulten.com/en/products/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](https://www.brightonbest.com/download/pds/PDS_Metric_Serrated_Hex_Flange_Nuts.pdf)

| 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](https://www.brightonbest.com/download/pds/PDS_Metric_Serrated_Hex_Flange_Nuts.pdf)

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](https://www.bossard.com/global-en/eshop/metallic-locking-nut/hex-nuts-with-flange-and-serrations/p/20230/), [Bossard BN 14476](https://www.bossard.com/global-en/eshop/hex-nuts/hex-flange-nuts/p/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](https://www.iso.org/standard/61525.html), [ISO 7044:2012](https://www.iso.org/standard/61526.html)

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](https://nylok.com/our-resources/fastener-glossary/), [Bossard BN 20230 functional principle](https://www.bossard.com/global-en/eshop/metallic-locking-nut/hex-nuts-with-flange-and-serrations/p/20230/)

## 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](../index.md).