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Hex Head Bolt Dimensions (ISO 4014 / DIN 931, M3 to M36)
Guide · Updated October 28, 2026
ISO 4014 covers partially threaded hexagon head bolts, product grades A and B; it replaced DIN 931. Values agree across fasten.it (DIN EN ISO 4014), Westfield Fasteners and the ISO 4014 published table. s and k are nominal; b is reference thread length.
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Step by step
- Find the thread: Pick the row for your thread size, M3 to M36.
- Pick the b column: Use the column for the bolt length l: up to 125, 125 to 200, or over 200 mm.
- Work out the shank: Plain shank is roughly l minus b; keep the shear plane on the shank, not the thread.
- Pick the spanner: Use s for the wrench size, e.g. 13 mm for M8.
ISO 4014 hex head bolt dimensions (mm)
Columns: thread d, pitch P, width across flats s, head height k nom., thread length b (ref.) for l ≤ 125, 125 < l ≤ 200 and l > 200 mm.
- Size | P | s | k | b ≤125 | b ≤200 | b >200
- M3 | 0.5 | 5.5 | 2 | 12 | 18 | 31
- M4 | 0.7 | 7 | 2.8 | 14 | 20 | 33
- M5 | 0.8 | 8 | 3.5 | 16 | 22 | 35
- M6 | 1 | 10 | 4 | 18 | 24 | 37
- M8 | 1.25 | 13 | 5.3 | 22 | 28 | 41
- M10 | 1.5 | 16 | 6.4 | 26 | 32 | 45
- M12 | 1.75 | 18 | 7.5 | 30 | 36 | 49
- M14 | 2 | 21 | 8.8 | 34 | 40 | 53
- M16 | 2 | 24 | 10 | 38 | 44 | 57
- M18 | 2.5 | 27 | 11.5 | 42 | 48 | 61
- M20 | 2.5 | 30 | 12.5 | 46 | 52 | 65
- M22 | 2.5 | 34 | 14 | 50 | 56 | 69
- M24 | 3 | 36 | 15 | 54 | 60 | 73
- M27 | 3 | 41 | 17 | 60 | 66 | 79
- M30 | 3.5 | 46 | 18.7 | 66 | 72 | 85
- M33 | 3.5 | 50 | 21 | — | 78 | 91
- M36 | 4 | 55 | 22.5 | — | 84 | 97
Worked example: M10 x 80 bolt
An M10 x 80 ISO 4014 bolt is under 125 mm long, so b is 26 mm and the plain shank is about 54 mm. It takes a 16 mm spanner and the head is 6.4 mm tall.
Common problems
- Nut will not tighten: thread length b too short for a thin clamp; use a shorter bolt or ISO 4017 full thread.
- Thread in the shear plane: pick a length so the plain shank passes through the joint.
- Spanner does not fit: old DIN 931 M10/M12/M14/M22 bolts have different flats.
FAQ
ISO 4014 vs ISO 4017?
Same hex head (s, k). ISO 4014 bolts are partly threaded with a plain shank; ISO 4017 screws are threaded to the head. Short lengths are only made as ISO 4017.
Is DIN 931 the same as ISO 4014?
ISO 4014 replaced DIN 931. DIN 931 used larger flats at M10, M12, M14 and M22 (17, 19, 22, 32 vs ISO 16, 18, 21, 34 mm).
Why is b dashed for M33 and M36 up to 125 mm?
No standard lengths that short exist for those sizes; some catalogs still print the formula value.
How is b worked out?
b is about 2d + 6, 2d + 12 or 2d + 25 mm for the three length bands; the chart gives the published values.
Related guides and calculators
- Grade C hex bolts (ISO 4016)
- Grade C hex nuts (ISO 4034)
- Fine thread hex bolts (ISO 8765)
- Fine thread hex screws (ISO 8676)
- Hex head screws (ISO 4017)
- Hex nuts (ISO 4032)
- Socket head cap screws (ISO 4762)
- All free machinist calculators
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