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Hex Flange Nut Dimensions (ISO 4161, M5 to M20)

Guide · Updated October 28, 2026

ISO 4161 covers hexagon nuts with flange, style 2: a hex nut with a round bearing flange formed on one face, so it acts like a nut and washer in one part. The table gives coarse pitch, width across flats s (wrench size) max and min, nut height m max and min, wrenching height mw min, width across corners e min, flange diameter dc max, bearing face dw min and flange thickness c min. Values agree between the ISO 4161:2012 preview table, the Nufast ISO 4161 production drawing and, for s, e, m max and dc, the RC Fastener ISO 4161 spec sheet. The fasteners.eu DIN 6923 table matches s, e, dc, dw and c. Conflicts: RC Fastener and DIN 6923 round m min to one decimal (7.6, 9.6, 11.6) and give 18.9 at M20, while ISO 4161 lists 7.64, 9.64, 11.57 and 18.70; the ISO values are shown. DIN 6923 also lists s min 29.67 at M20 versus 29.16 in ISO 4161, and a different wrenching height; ISO values are used. Serrated flange nuts and fine thread versions are not covered here.

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Step by step

  1. Match the thread: Check diameter and pitch with a thread gage. ISO 4161 is coarse pitch M5 to M20 only.
  2. Pick the wrench: Across flats s max is the wrench size: M6 10 mm, M8 13 mm, M10 15 mm, M12 18 mm, M16 24 mm. Note M10 is 15 mm, not 16 mm like a plain ISO 4032 nut.
  3. Check the flange: The flange diameter dc max sets the spot face or counterbore you need. Size a spot face at least 1 mm over dc max.
  4. Check the height: Nut height m max equals the thread diameter (M10 nut is 10 mm high including the flange).
  5. Skip the washer: The flange spreads the load like a washer, so a separate flat washer is usually not needed on steel. Soft or slotted parts may still need a large washer.
  6. Leave thread past the nut: Run at least 2 full threads past the nut face.

ISO 4161 hex flange nut dimensions (mm)

Columns: thread size, coarse pitch P, width across flats s max and min (s max is the wrench size), nut height m max, m min, wrenching height mw min, width across corners e min, flange diameter dc max, bearing face diameter dw min, flange thickness c min. Grade A through M16, grade B for M20. M14 is a second choice size.

Flange nut vs plain nut and washer

An M8 ISO 4161 flange nut has a 17.9 mm max flange and is 8.00 mm high. A plain ISO 4032 M8 nut (6.80 mm max) plus an ISO 7089 washer (1.6 mm thick, 16 mm OD) stacks to about 8.4 mm with a 16 mm bearing. The flange nut is one part, slightly shorter, with a similar bearing face.

Worked example: bolt length for an M10 flange nut

Clamping a 6 mm bracket to a 10 mm plate: grip 16 mm, nut m max 10.00 mm, plus 2 threads at 1.5 mm = 3 mm. Total 29 mm, so an M10 x 30 works.

Common problems

FAQ

What wrench fits an M10 flange nut?

15 mm for ISO 4161 and DIN 6923. A plain ISO 4032 M10 nut is 16 mm, so do not mix them up.

Is DIN 6923 the same as ISO 4161?

They share wrench size, flange diameter and height max. Some minor values differ, for example m min and wrenching height, so check the drawing when it matters.

Do flange nuts need a washer?

Usually not. The flange works as a built in washer. Serrated flange nuts also resist loosening but mark the surface.

What is ISO 10663?

ISO 10663 is the fine pitch version of this plain flange nut (M8x1 to M20x1.5), with the same hex and flange sizes.

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