DIN 931 is the legacy German designation for the partially threaded hexagon head bolt. The current standard is DIN EN ISO 4014 / ISO 4014:2022 — the heads and thread lengths match, but the width across flats differs at M10, M12, M14 and M22. This page gives the DIN 931 dimension tables, the thread length b for lengths up to 125 mm, and the exact difference from ISO 4014 so the bolt and nut are quoted to the same standard.
| Parameter (mm) | M3 | M4 | M5 | M6 | M8 | M10 | M12 | M14 | M16 | M18 |
|---|---|---|---|---|---|---|---|---|---|---|
| P — pitch (mm) | 0.5 | 0.7 | 0.8 | 1 | 1.25 | 1.5 | 1.75 | 2 | 2 | 2.5 |
| k — head height | 2 | 2.8 | 3.5 | 4 | 5.3 | 6.4 | 7.5 | 8.8 | 10 | 11.5 |
| c — max | 0.4 | 0.4 | 0.5 | 0.5 | 0.6 | 0.6 | 0.6 | 0.6 | 0.8 | 0.8 |
| c — min | 0.15 | 0.15 | 0.15 | 0.15 | 0.15 | 0.15 | 0.15 | 0.15 | 0.2 | 0.2 |
| r — min | 0.1 | 0.2 | 0.2 | 0.25 | 0.4 | 0.4 | 0.6 | 0.6 | 0.6 | 0.6 |
| s (across flats) — DIN 931 | 5.5 | 7 | 8 | 10 | 13 | 17 | 19 | 22 | 24 | 27 |
| e (across corners) — DIN 931 | 6.01 | 7.66 | 8.79 | 11.05 | 14.38 | 18.9 | 21.1 | 24.49 | 26.75 | 30.14 |
| b — thread length, lengths ≤ 125 mm | 12 | 14 | 16 | 18 | 22 | 26 | 30 | 34 | 38 | 42 |
Source: DIN 931 / ISO 4014 compiled table (see Sources). Head dimensions (k, c, r) verified identical to ISO 4017:2022 for all 20 sizes; across-flats differ from ISO 4014 for M10, M12, M14 and M22 — see section 4.
| Parameter (mm) | M20 | M22 | M24 | M27 | M30 | M36 | M42 | M48 | M56 | M64 |
|---|---|---|---|---|---|---|---|---|---|---|
| P — pitch (mm) | 2.5 | 2.5 | 3 | 3 | 3.5 | 4 | 4.5 | 5 | 5.5 | 6 |
| k — head height | 12.5 | 14 | 15 | 17 | 18.7 | 22.5 | 26 | 30 | 35 | 40 |
| c — max | 0.8 | 0.8 | 0.8 | 0.8 | 0.8 | 0.8 | 1 | 1 | 1 | 1 |
| c — min | 0.2 | 0.2 | 0.2 | 0.2 | 0.2 | 0.2 | 0.3 | 0.3 | 0.3 | 0.3 |
| r — min | 0.8 | 0.8 | 0.8 | 1 | 1 | 1 | 1.2 | 1.6 | 2 | 2 |
| s (across flats) — DIN 931 | 30 | 32 | 36 | 41 | 46 | 55 | 65 | 75 | 85 | 95 |
| e (across corners) — DIN 931 | 33.53 | 38.85 | 39.98 | 45.2 | 50.85 | 60.79 | 71.3 | 82.6 | 93.56 | 104.9 |
| b — thread length, lengths ≤ 125 mm | 46 | 50 | 54 | 60 | 66 | — | — | — | — | — |
Source: DIN 931 / ISO 4014 compiled table (see Sources). Head dimensions (k, c, r) verified identical to ISO 4017:2022 for all 20 sizes; across-flats differ from ISO 4014 for M10, M12, M14 and M22 — see section 4.
The last row of each table gives b for bolts up to 125 mm long — for example a DIN 931 M10 × 100 has b = 26 mm. For longer lengths the thread length increases according to the standard’s length tables; those are not reproduced here. Tell us the size and length and we confirm the thread length, or send the drawing.
Bolts are quoted in steel classes 8.8, 10.9 and 12.9, and in stainless A2 / A4. Property class selection refers to ISO 898-1 for steel and ISO 3506-1 for stainless steel. Standard finishes: zinc plating, hot-dip galvanizing, zinc-nickel and dacromet. See mechanical properties and surface treatment.
State the standard (DIN 931 or ISO 4014:2022), size × length, property class or stainless grade, finish and quantity. Because of the across-flats differences, also state which standard the matching nut follows.
Mostly — but not exactly. The heads and thread lengths match, yet the width across flats (s) and across corners (e) differ for M10, M12, M14 and M22. DIN 931 M10 has s = 17 mm while ISO 4014 uses s = 16 mm; at M22 it is the other way round (DIN 32 mm vs ISO 34 mm). Check which standard the drawing means before quoting.
DIN 931 is partially threaded (a plain shank section, thread length b); DIN 933 is fully threaded. Head dimensions are the same; choose DIN 931 where the drawing shows a shank.
b is the thread length. This page gives the b value used for lengths up to 125 mm. For longer bolts the thread length changes according to the standard’s length tables — tell us the length and we confirm the thread length.
Use a nut called out to the same standard as the bolt. Because DIN 931 differs from ISO 4014 at M10/M12/M14/M22, mixing a DIN 931 bolt with an ISO 4032 nut at those sizes gives a mismatched across-flats pair — quote both to the same standard.
M3 to M64 in this table. ISO 4014:2022 also covers M1.6–M2.5, which DIN 931 did not include.
Property class selection refers to ISO 898-1 for steel and ISO 3506-1 for stainless steel; common classes are 8.8, 10.9 and 12.9, and A2 / A4 stainless. Confirm the class on the drawing or order.
Carbon steel and stainless steel (A2 / A4) with zinc plating, hot-dip galvanizing, zinc-nickel or dacromet. See surface treatment for coating comparisons.
DIN 931 is a legacy designation; the current standard is DIN EN ISO 4014 / ISO 4014:2022. Many drawings still say DIN 931 — quote either designation, but watch the across-flats differences above.
Dimensions: DIN 931 / ISO 4014 compiled table (source: fasteners.eu, retrieved 2026-10-28). Head dimensions k, c and r verified identical to ISO 4017:2022 for all 20 sizes (80/80 checks); across-flats/corners differences at M10/M12/M14/M22 taken from the DIN 931 table’s ISO 4014 comparison rows. Thread length b for lengths ≤ 125 mm cross-checked against ISO 4014:2022 for M1.6–M12. Longer-length thread tables are not reproduced. Per-size pages: DIN 931 size chart. Page last reviewed: 2026-10-30.
Bolt Weight Calculator — theoretical weight from the standard’s dimensions →