Flange nut (hex flange nut)

01

Fix the standard, size and flange type

CDE Fasteners' datasheet for DIN 6923 / ISO 4161 serrated hex flange nuts describes a hex nut with an enlarged circular base whose serrated bearing face displaces material on the mating surface when tightened, so that more torque is needed to loosen than to tighten. It says the flange spans oversized or poorly aligned holes, gives a more uniform bearing-stress to clamp-force ratio than other low-carbon lock nuts and does not gall threads. Its table lists sizes M3 to M20: for example M6 with 10.00 mm across flats, 6.0 mm maximum height and a 14.2 mm maximum flange; M10 with 15.00 mm, 10.0 mm and 21.8 mm; and M20 with 30.00 mm, 20.0 mm and 42.8 mm. [1]

Haiyan Bolt, a linked supplier, lists hex flange nuts to DIN 6923, ASTM A563 A and ASME B18.2.2, in UNC and UNF inch threads and metric sizes M5 to M33, in carbon, alloy and stainless steels (201, 304, 316), brass and aluminium alloy. [2]

Editorial calculation: the M10 nut's 21.8 mm maximum flange is about 21.8 / 15 ≈ 1.45 times its 15 mm width across flats, which is where the larger bearing area comes from; check that the flange diameter fits next to walls or other fasteners in your joint.

Give the supplier the standard (DIN 6923, ISO 4161, ASME B18.2.2 or drawing), thread size and pitch, serrated or plain flange, property class or grade, material, finish and coating thickness, mating bolt class, quantity and packing, and any certificates (material, proof load, coating).

02

Set the property class, proof load and finish

CDE lists Class 8 steel nuts with composition limits of carbon 0.58% maximum, manganese 0.25% minimum, phosphorus 0.060% maximum and sulfur 0.150% maximum, no heat treatment required below 18 mm, hardness HV 188–302 for M5 to M16, and proof load stresses of 117,450 psi (M5–M6), 120,350 psi (M8–M10) and 121,800 psi (M12–M16); Class A2-50 stainless nuts, for use with stainless bolts, have a proof load stress of 72,500 psi. [1]

Haiyan lists finishes from plain, black oxide and zinc plating to hot-dip galvanising, nickel and chrome plating, Dacromet and Geomet, and grades including SAE 2 and 5, ASTM A194 2H and metric classes 4 to 10. [2]

Editorial calculation: 120,350 psi × 0.006895 ≈ 830 MPa proof stress for M8–M10 Class 8 nuts, and 72,500 psi ≈ 500 MPa for A2-50. Pair the nut class with the bolt property class and confirm the proof load test on the certificate.

03

Check that your size falls inside the ISO 4161 scope

BSI's catalogue page for BS ISO 4161:2012, published 30 September 2012, marked current and identical to ISO 4161:2012, states the standard's scope: hexagon nuts with flange (style 2) with metric coarse threads from M5 to M20 inclusive, product grade A for threads up to and including M16 and product grade B for threads above M16. Where other specifications are required in special cases, it says they can be selected from existing International Standards, for example ISO 261, ISO 724, ISO 898-2, ISO 965-2 and ISO 3506-2. [4]

Editorial reading: the CDE datasheet table runs from M3 to M20 under the DIN 6923 / ISO 4161 heading, and the linked supplier above offers metric sizes from M5 to M33. M3, M4 and sizes above M20 therefore fall outside the ISO 4161 scope that BSI states; for those sizes, name DIN 6923 or your drawing in the order. For M20 nuts, ask whether the supplier makes them to product grade B, the grade ISO 4161 sets above M16. [1] [2] [4]

04

Check inch-series serrated flange nut dimensions

Fastenerdata's record for the UNC serrated hexagon flange nut in case-hardened SAE grade 5 steel to IFI 145 covers sizes No. 6 to 3/4 in and tabulates dimensions by column letter. For the 1/4 in nut it gives f 0.428–0.438 in, g 0.488–0.505 in, b 0.574–0.594 in and h 0.222–0.236 in; for 1/2 in, f 0.736–0.750 in, b 1.000–1.031 in and h 0.437–0.458 in; for 3/4 in, f 1.088–1.125 in, b 1.460–1.500 in and h 0.627–0.675 in. The site also lists stainless serrated and plain and large-flange steel versions to IFI 145. [3]

Compare the inch series with the DIN 6923 / ISO 4161 metric data and Class 8 proof stresses above, and with the standards and finishes a supplier quotes. [1] [2] [3]

Editorial reading and calculation: the f column matches standard across-flats sizes (0.438 in = 7/16 in for 1/4 in nuts) and the b column is the largest dimension, consistent with the flange diameter; confirm letters against the drawing. On that reading the 1/4 in nut's 0.594 in flange is about 15.1 mm and the 1/2 in nut's 1.031 in flange about 26.2 mm.

For inch-series nuts, ask which standard (IFI 145 or ASME B18.2.2), grade and case-hardening the supplier applies, and get the flange diameter and thickness for your size.

05

Compare what suppliers offer

Suppliers linked to this page list hex flange nuts; each card links to the page reviewed.

Listings include DIN 6923 hex flange nuts from fastener makers, hex flange nuts alongside bolts and washers, and flange nuts for mould clamping kits. A nut tapping machine maker and sites that could not be reached are hidden here. Ask each for standard, class, finish, certificates and minimum order.

06

Trace the nut features

This is a functional reference built from the sources cited; it is not one maker's specification.

07

Fill the specification fields with values for your joint

A flange nut quotation needs values for your joint. The table explains each field, gives published values where a reviewed source states them, and says what to obtain from the supplier.

08

Send the standard, size and class data together

Paste it into your enquiry below or into an email to a maker, then replace every bracket.

Standard: [DIN 6923; ISO 4161; ASME B18.2.2]
Size: [thread; pitch]
Flange: [serrated; plain]
Class: [8; 10; A2-50; SAE grade]
Finish: [type; thickness]
Quantity: [lot; packing]
Certificates: [material; proof load; coating]

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