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Fine Thread Hex Nut Dimensions (ISO 8673, M8x1 to M36x3)

Guide · Updated October 28, 2026

ISO 8673 covers hexagon regular nuts, style 1, with metric fine pitch thread, product grade A up to M16 and grade B from M18. Hex, height and corner sizes match the coarse thread ISO 4032 nut. Every value below agrees across three sources: the ISO 8673:2023 preview table (M8 to M16 in full), the fasteners.eu ISO 8673 table and the DigiPich ISO 8673 table; the Dueemme Sidol ISO 8673 table confirms s and m for every size including the 2023 pitch pairings. Not shown: transition diameter da, because the 2023 edition rounds da max differently (for example M12 12.96 vs 13.00 mm) from older tables. Sizes over M36 are historical in the 2023 edition and are left out.

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Step by step

  1. Confirm fine pitch: Check pitch with a thread gage. An M12x1.5 nut will not run on a coarse M12x1.75 bolt, and M10x1 vs M10x1.25 look alike.
  2. Pick the wrench: Same hex as ISO 4032: M8 13 mm, M10 16 mm, M12 18 mm, M16 24 mm, M20 30 mm, M24 36 mm.
  3. Check the height: Use m max for bolt length math; it matches the coarse ISO 4032 nut size for size.
  4. Check the bearing face: Seat diameter must clear dw min (M12 is 16.63 mm) for full bearing.
  5. Need a taller nut?: ISO 8674 is the style 2 (taller) fine pitch hex nut; ISO 8675 is the thin fine pitch nut.
  6. Leave thread past the nut: Run at least 2 full threads past the nut face.

ISO 8673 fine thread hex 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, bearing face diameter dw min. Sizes in parentheses are non-preferred in ISO 8673:2023.

Fine vs coarse hex nut

An M12x1.5 ISO 8673 nut and an M12 ISO 4032 nut (1.75 pitch) are both 18 mm hex and 10.80 mm max high. Only the thread differs, so keep them in separate bins and check pitch before assembly.

Worked example: bolt length for an M16x1.5 nut

Grip 25 mm, nut m max 14.80 mm, plus 2 threads at 1.5 mm = 3.0 mm. Total 42.8 mm, so an M16x1.5 x 45 works.

Common problems

FAQ

What is the difference between ISO 8673 and ISO 4032?

Same hex, height and corners size for size. ISO 8673 has metric fine pitch thread; ISO 4032 has coarse thread.

What is the difference between ISO 8673 and ISO 8674?

ISO 8673 is style 1 (regular height). ISO 8674 is style 2, a taller nut with the same hex.

Is ISO 8673 the same as DIN 934 fine?

Close but not identical. DIN 934 used 17 mm hex for M10 and 19 mm for M12 in older editions; ISO 8673 uses 16 and 18 mm.

What wrench fits an M12x1.5 hex nut?

18 mm.

Which pitch is preferred?

ISO 8673:2023 lists M10x1.25, M12x1.5, M20x2 as first choice; M10x1, M12x1.25, M20x1.5 and the sizes in parentheses are non-preferred.

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