Across flats (the wrench), head height and thread length for metric hex cap screws M3 to M36 — DIN 933 and DIN 931 — plus tensile stress area.
The numbers behind a metric hex cap screw. DIN 933 is threaded the full length; DIN 931 has a plain shank and a thread length b. The fine-thread versions, DIN 961 and DIN 960, have the same heads. Across flats s is your wrench size. Sizes are in millimeters.
Letters match the table columns. s across flats (the wrench size), k head height, l length from under the head, b thread length on a DIN 931 screw, d thread diameter. Metric heads are marked with their property class (8.8, 10.9, 12.9).
| Size | Pitch (coarse) | Across flats s (wrench) | s min | Head height k | k min / max |
|---|---|---|---|---|---|
| M3 | 0.5 | 5.5 mm | 5.32 | 2 mm | 1.88 / 2.12 |
| M4 | 0.7 | 7 mm | 6.78 | 2.8 mm | 2.68 / 2.92 |
| M5 | 0.8 | 8 mm | 7.78 | 3.5 mm | 3.35 / 3.65 |
| M6 | 1 | 10 mm | 9.78 | 4 mm | 3.85 / 4.15 |
| M8 | 1.25 | 13 mm | 12.73 | 5.3 mm | 5.15 / 5.45 |
| M10 | 1.5 | 17 mm | 16.73 | 6.4 mm | 6.22 / 6.58 |
| M12 | 1.75 | 19 mm | 18.67 | 7.5 mm | 7.32 / 7.68 |
| M14 | 2 | 22 mm | 21.67 | 8.8 mm | 8.62 / 8.98 |
| M16 | 2 | 24 mm | 23.67 | 10 mm | 9.82 / 10.18 |
| M18 | 2.5 | 27 mm | 26.67 | 11.5 mm | 11.28 / 11.72 |
| M20 | 2.5 | 30 mm | 29.67 | 12.5 mm | 12.28 / 12.72 |
| M22 | 2.5 | 32 mm | 31.61 | 14 mm | 13.78 / 14.22 |
| M24 | 3 | 36 mm | 35.38 | 15 mm | 14.78 / 15.22 |
| M27 | 3 | 41 mm | 40 | 17 mm | 16.65 / 17.35 |
| M30 | 3.5 | 46 mm | 45 | 18.7 mm | 18.28 / 19.12 |
| M33 | 3.5 | 50 mm | 49 | 21 mm | 20.58 / 21.42 |
| M36 | 4 | 55 mm | 53.8 | 22.5 mm | 22.08 / 22.92 |
DIN vs. ISO: ISO 4017 / 4014 heads are the same except across the flats at M10, M12, M14 and M22 — check which one you have before you grab a wrench. M27 and up are made to product grade B; their minimums are grade B.
| Size | l up to 125 mm | l over 125, up to 200 mm | l over 200 mm |
|---|---|---|---|
| M3 | 12 mm | — | — |
| M4 | 14 mm | — | — |
| M5 | 16 mm | 22 mm | — |
| M6 | 18 mm | 24 mm | — |
| M8 | 22 mm | 28 mm | — |
| M10 | 26 mm | 32 mm | 45 mm |
| M12 | 30 mm | 36 mm | 49 mm |
| M14 | 34 mm | 40 mm | 53 mm |
| M16 | 38 mm | 44 mm | 57 mm |
| M18 | 42 mm | 48 mm | 61 mm |
| M20 | 46 mm | 52 mm | 65 mm |
| M22 | 50 mm | 56 mm | 69 mm |
| M24 | 54 mm | 60 mm | 73 mm |
| M27 | 60 mm | 66 mm | 79 mm |
| M30 | 66 mm | 72 mm | 85 mm |
| M33 | 72 mm | 78 mm | 91 mm |
| M36 | 78 mm | 84 mm | 97 mm |
A DIN 933 screw is threaded all the way to the head instead. When the screw is shorter than the thread length, it is threaded the full length.
| Thread | Series | Pitch (mm) | Stress area |
|---|---|---|---|
| M1 | Coarse | 0.25 | 0.5 |
| M1.1 | Coarse | 0.25 | 0.6 |
| M1.2 | Coarse | 0.25 | 0.7 |
| M1.4 | Coarse | 0.3 | 1.0 |
| M1.6 | Coarse | 0.35 | 1.3 |
| M1.8 | Coarse | 0.35 | 1.7 |
| M2 | Coarse | 0.4 | 2.1 |
| M2.2 | Coarse | 0.45 | 2.5 |
| M2.5 | Coarse | 0.45 | 3.4 |
| M3 | Coarse | 0.5 | 5.0 |
| M3.5 | Coarse | 0.6 | 6.8 |
| M4 | Coarse | 0.7 | 8.8 |
| M5 | Coarse | 0.8 | 14.2 |
| M6 | Coarse | 1 | 20.1 |
| M7 | Coarse | 1 | 28.9 |
| M8 | Coarse | 1.25 | 36.6 |
| M9 | Coarse | 1.25 | 48.1 |
| M10 | Coarse | 1.5 | 58.0 |
| M11 | Coarse | 1.5 | 72.3 |
| M12 | Coarse | 1.75 | 84.3 |
| M14 | Coarse | 2 | 115.4 |
| M16 | Coarse | 2 | 156.7 |
| M18 | Coarse | 2.5 | 192.5 |
| M20 | Coarse | 2.5 | 244.8 |
| M22 | Coarse | 2.5 | 303.4 |
| M24 | Coarse | 3 | 352.5 |
| M27 | Coarse | 3 | 459.4 |
| M30 | Coarse | 3.5 | 560.6 |
| M33 | Coarse | 3.5 | 693.6 |
| M36 | Coarse | 4 | 816.7 |
| M39 | Coarse | 4 | 975.8 |
| M42 | Coarse | 4.5 | 1120.9 |
| M45 | Coarse | 4.5 | 1306.0 |
| M48 | Coarse | 5 | 1473.2 |
| M52 | Coarse | 5 | 1757.8 |
| M56 | Coarse | 5.5 | 2030.0 |
| M1×0.2 | Fine | 0.2 | 0.5 |
| M2×0.25 | Fine | 0.25 | 2.4 |
| M4×0.35 | Fine | 0.35 | 10.6 |
| M4×0.5 | Fine | 0.5 | 9.8 |
| M5×0.5 | Fine | 0.5 | 16.1 |
| M6×0.5 | Fine | 0.5 | 24.0 |
| M6×0.75 | Fine | 0.75 | 22.0 |
| M7×0.75 | Fine | 0.75 | 31.1 |
| M8×0.5 | Fine | 0.5 | 44.5 |
| M8×0.75 | Fine | 0.75 | 41.8 |
| M8×1.0 | Fine | 1 | 39.2 |
| M9×0.75 | Fine | 0.75 | 54.1 |
| M9×1.0 | Fine | 1 | 51.0 |
| M10×0.75 | Fine | 0.75 | 67.9 |
| M10×1.0 | Fine | 1 | 64.5 |
| M10×1.25 | Fine | 1.25 | 61.2 |
| M11×0.75 | Fine | 0.75 | 83.3 |
| M11×1.0 | Fine | 1 | 79.5 |
| M12×1.0 | Fine | 1 | 96.1 |
| M12×1.25 | Fine | 1.25 | 92.1 |
| M12×1.5 | Fine | 1.5 | 88.1 |
| M14×1.0 | Fine | 1 | 134.0 |
| M14×1.25 | Fine | 1.25 | 129.2 |
| M14×1.5 | Fine | 1.5 | 124.5 |
| M15×1.0 | Fine | 1 | 155.3 |
| M15×1.5 | Fine | 1.5 | 145.1 |
| M16×1.0 | Fine | 1 | 178.2 |
| M16×1.5 | Fine | 1.5 | 167.2 |
| M17×1.0 | Fine | 1 | 202.6 |
| M17×1.5 | Fine | 1.5 | 191.0 |
| M18×1.0 | Fine | 1 | 228.6 |
| M18×1.5 | Fine | 1.5 | 216.2 |
| M18×2.0 | Fine | 2 | 204.2 |
| M20×1.0 | Fine | 1 | 285.4 |
| M20×1.5 | Fine | 1.5 | 271.5 |
| M20×2.0 | Fine | 2 | 258.0 |
| M22×1.0 | Fine | 1 | 348.4 |
| M22×1.5 | Fine | 1.5 | 333.1 |
| M22×2.0 | Fine | 2 | 318.1 |
| M24×1.0 | Fine | 1 | 417.7 |
| M24×1.5 | Fine | 1.5 | 400.9 |
| M24×2.0 | Fine | 2 | 384.4 |
| M25×1.0 | Fine | 1 | 454.7 |
| M25×1.5 | Fine | 1.5 | 437.2 |
| M25×2.0 | Fine | 2 | 420.0 |
| M26×1.5 | Fine | 1.5 | 475.0 |
| M27×1.0 | Fine | 1 | 533.5 |
| M27×1.5 | Fine | 1.5 | 514.4 |
| M27×2.0 | Fine | 2 | 495.7 |
| M28×1.0 | Fine | 1 | 575.2 |
| M28×1.5 | Fine | 1.5 | 555.4 |
| M28×2.0 | Fine | 2 | 536.0 |
| M30×1.5 | Fine | 1.5 | 642.1 |
| M30×2.0 | Fine | 2 | 621.2 |
| M33×2.0 | Fine | 2 | 760.8 |
| M36×3.0 | Fine | 3 | 864.9 |
| M39×3.0 | Fine | 3 | 1028.4 |
| M42×3.0 | Fine | 3 | 1206.0 |
| M45×3.0 | Fine | 3 | 1397.7 |
| M48×3.0 | Fine | 3 | 1603.6 |
| M52×4.0 | Fine | 4 | 1828.2 |
The area a screw’s strength works over: load in newtons = stress area × the class’s strength in MPa. Example: an M10 8.8 has 58.0 mm² × 800 MPa = about 46,400 N minimum tensile. Worked out as 0.7854 × (d − 0.9382 × P)² (ISO 898-1), from the metric thread chart.
| Size | Wrench s | Flange dia dc max | Head height k max |
|---|---|---|---|
| M5 | 8 mm | 11.8 | 6.2 |
| M6 | 10 mm | 14.2 | 7.3 |
| M8 | 13 mm | 17.9 | 9.4 |
| M10 | 15 mm | 21.8 | 11.4 |
| M12 | 18 mm | 26 | 13.8 |
| M14 | 21 mm | 29.9 | 15.9 |
| M16 | 24 mm | 34.5 | 18.3 |
| M20 | 30 mm | 42.8 | 22.4 |
A hex head with a built-in washer face (often serrated to resist loosening). Head height k includes the flange. Stress area and class strength are the same as for a hex cap screw of the same thread.
Strength and marking
Metric hex caps are marked on the head with their property class — 8.8, 10.9 or 12.9. What each class guarantees is on the ISO 898-1 page. The inch version of this chart is hex cap screw dimensions; not sure if a bolt is metric? See metric vs. inch.
Quick answers
- What size wrench fits an M10 bolt?
- An M10 hex cap screw (DIN 933 / 931) takes a 17 mm wrench.
- What wrench size goes with each metric bolt size?
- Across the flats: M3 – 5.5 mm, M4 – 7 mm, M5 – 8 mm, M6 – 10 mm, M8 – 13 mm, M10 – 17 mm, M12 – 19 mm, M14 – 22 mm, M16 – 24 mm, M18 – 27 mm, M20 – 30 mm, M22 – 32 mm, M24 – 36 mm, M27 – 41 mm, M30 – 46 mm, M33 – 50 mm, M36 – 55 mm (DIN 933 / 931).
- What is the thread pitch of an M12 bolt?
- M12 coarse thread is 1.75 mm pitch. Each coarse pitch is in the table above.
- How tall is the head of an M8 hex cap screw?
- About 5.3 mm (5.15–5.45 mm).
- How long is the thread on a metric hex cap screw?
- On a partially threaded screw up to 125 mm long, the thread length is set by size — for example 22 mm on M8 and 26 mm on M10.