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Fine Thread Hex Flange Nut Dimensions (ISO 10663, M8x1 to M20x1.5)

Guide · Updated October 28, 2026

ISO 10663 covers hexagon nuts with flange, style 2, with metric fine pitch thread from M8x1 to M20x1.5, grade A through M16 and grade B for M20. The hex and flange match the coarse thread ISO 4161 nut. Every value below agrees across three sources: the ISO 10663:2012 preview table, the ISO 10663:1999 preview table and the Engineering Hardware ISO 10663 table (the AMESweb ISO 10663 calculator lists the same columns). No conflicts were found. Width across flats s, nut height m, wrenching height mw, across corners e, flange diameter dc, bearing face dw and flange thickness c are shown. Not covered: serrated flange nuts and prevailing torque (nylon insert or all metal) fine pitch flange nuts, which are separate standards.

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Step by step

Confirm fine pitch: Check pitch with a thread gage. M10 comes as 1.25 (preferred) or 1; M12 as 1.25 (preferred) or 1.5. A coarse M10x1.5 bolt will not take an ISO 10663 nut.
Pick the wrench: Same hex as ISO 4161: M8 13 mm, M10 15 mm, M12 18 mm, M16 24 mm, M20 30 mm.
Check the flange: Size a spot face at least 1 mm over dc max (M12 is 26.0 mm).
Check the height: Nut height m max equals the nominal diameter, flange included.
Choose a locking method if needed: ISO 10663 is a plain flange nut. Nylon insert or all metal lock versions are ordered separately (for example ISO 12125/12126).
Leave thread past the nut: Run at least 2 full threads past the nut face.

ISO 10663 fine thread hex flange nut dimensions (mm)

Columns: thread size x pitch, 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. Sizes in parentheses are second choice.

Size | s max | s min | m max | m min | mw min | e min | dc max | dw min | c min
M8x1 | 13.00 | 12.73 | 8.00 | 7.64 | 4.6 | 14.38 | 17.9 | 15.8 | 1.2
M10x1.25 | 15.00 | 14.73 | 10.00 | 9.64 | 5.6 | 16.64 | 21.8 | 19.6 | 1.5
(M10x1) | 15.00 | 14.73 | 10.00 | 9.64 | 5.6 | 16.64 | 21.8 | 19.6 | 1.5
M12x1.25 | 18.00 | 17.73 | 12.00 | 11.57 | 6.8 | 20.03 | 26.0 | 23.8 | 1.8
(M12x1.5) | 18.00 | 17.73 | 12.00 | 11.57 | 6.8 | 20.03 | 26.0 | 23.8 | 1.8
(M14x1.5) | 21.00 | 20.67 | 14.00 | 13.30 | 7.7 | 23.36 | 29.9 | 27.6 | 2.1
M16x1.5 | 24.00 | 23.67 | 16.00 | 15.30 | 8.9 | 26.75 | 34.5 | 31.9 | 2.4
M20x1.5 | 30.00 | 29.16 | 20.00 | 18.70 | 10.7 | 32.95 | 42.8 | 39.9 | 3.0

Fine vs coarse flange nut

An M12x1.25 ISO 10663 nut and an M12 ISO 4161 nut (1.75 pitch) look identical: 18 mm hex, 26.0 mm flange, 12.00 mm high. Only the thread differs, so keep them in separate bins and check pitch before assembly.

Worked example: bolt length for an M12x1.25 flange nut

Grip 20 mm, nut m max 12.00 mm, plus 2 threads at 1.25 mm = 2.5 mm. Total 34.5 mm, so an M12x1.25 x 35 works.

Common problems

Coarse bolt, fine nut: it starts, then binds after a turn. Check pitch first.
M10x1 vs M10x1.25: both exist; the 1.25 is preferred.
Flange hits a fillet: check dc max against the spot face.

FAQ

Is ISO 10663 a nylon insert lock nut?

No. ISO 10663 is a plain hex flange nut, style 2, with fine pitch thread. Fine pitch prevailing torque flange nuts are in separate standards such as ISO 12125 (nylon insert) and ISO 12126 (all metal).

Is ISO 10663 the same size as ISO 4161?

Yes for the shared sizes M8 to M20: same s, e, m, dc, dw and c. Only the thread pitch differs.

What wrench fits an M12x1.25 flange nut?

18 mm.

Which sizes should be avoided?

ISO lists M10x1, M12x1.5 and M14x1.5 in parentheses as second choice sizes.

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