M20 Bolt Torque
An M20 8.8 bolt with a coarse M20×2.5 thread needs about 424.9 N·m (313.4 ft·lb) when dry and 316.6 N·m (233.5 ft·lb) when oiled, tightened to 70% of yield (clamp force 109.7 kN).
| Grade | Clamp forcepreload | Dryμ 0.15 | Oiledμ 0.11 | PTFE / moly pasteμ 0.06 |
|---|---|---|---|---|
| 4.6 | 41.1 kN9245 lbf | 159.3 N·m117.5 ft·lb | 118.7 N·m87.6 ft·lb | 78.1 N·m57.6 ft·lb |
| 4.8 | 54.8 kN12327 lbf | 212.4 N·m156.7 ft·lb | 158.3 N·m116.8 ft·lb | 104.2 N·m76.9 ft·lb |
| 5.6 | 51.4 kN11557 lbf | 199.2 N·m146.9 ft·lb | 148.4 N·m109.5 ft·lb | 97.7 N·m72.0 ft·lb |
| 5.8 | 68.5 kN15409 lbf | 265.5 N·m195.9 ft·lb | 197.9 N·m146.0 ft·lb | 130.2 N·m96.1 ft·lb |
| 6.8 | 82.3 kN18491 lbf | 318.7 N·m235.0 ft·lb | 237.5 N·m175.2 ft·lb | 156.3 N·m115.3 ft·lb |
| 8.8 | 109.7 kN24654 lbf | 424.9 N·m313.4 ft·lb | 316.6 N·m233.5 ft·lb | 208.4 N·m153.7 ft·lb |
| 10.9 | 154.2 kN34670 lbf | 597.5 N·m440.7 ft·lb | 445.3 N·m328.4 ft·lb | 293.1 N·m216.1 ft·lb |
| 12.9 | 185.1 kN41604 lbf | 717.0 N·m528.8 ft·lb | 534.3 N·m394.1 ft·lb | 351.7 N·m259.4 ft·lb |
| A2-70 | 77.1 kN17335 lbf | 298.7 N·m220.3 ft·lb | 222.6 N·m164.2 ft·lb | 146.5 N·m108.1 ft·lb |
| A4-70 | 77.1 kN17335 lbf | 298.7 N·m220.3 ft·lb | 222.6 N·m164.2 ft·lb | 146.5 N·m108.1 ft·lb |
| A4-80 | 102.8 kN23113 lbf | 398.3 N·m293.8 ft·lb | 296.8 N·m218.9 ft·lb | 195.4 N·m144.1 ft·lb |
| Grade | Clamp forcepreload | Dryμ 0.15 | Oiledμ 0.11 | PTFE / moly pasteμ 0.06 |
|---|---|---|---|---|
| 4.6 | 45.6 kN10254 lbf | 171.9 N·m126.8 ft·lb | 126.2 N·m93.1 ft·lb | 80.5 N·m59.3 ft·lb |
| 4.8 | 60.8 kN13672 lbf | 229.3 N·m169.1 ft·lb | 168.3 N·m124.1 ft·lb | 107.3 N·m79.1 ft·lb |
| 5.6 | 57.0 kN12818 lbf | 214.9 N·m158.5 ft·lb | 157.8 N·m116.4 ft·lb | 100.6 N·m74.2 ft·lb |
| 5.8 | 76.0 kN17090 lbf | 286.6 N·m211.4 ft·lb | 210.3 N·m155.1 ft·lb | 134.1 N·m98.9 ft·lb |
| 6.8 | 91.2 kN20508 lbf | 343.9 N·m253.6 ft·lb | 252.4 N·m186.2 ft·lb | 160.9 N·m118.7 ft·lb |
| 8.8 | 121.6 kN27344 lbf | 458.5 N·m338.2 ft·lb | 336.5 N·m248.2 ft·lb | 214.6 N·m158.3 ft·lb |
| 10.9 | 171.0 kN38453 lbf | 644.8 N·m475.6 ft·lb | 473.3 N·m349.1 ft·lb | 301.7 N·m222.6 ft·lb |
| 12.9 | 205.3 kN46143 lbf | 773.7 N·m570.7 ft·lb | 567.9 N·m418.9 ft·lb | 362.1 N·m267.1 ft·lb |
| A2-70 | 85.5 kN19226 lbf | 322.4 N·m237.8 ft·lb | 236.6 N·m174.5 ft·lb | 150.9 N·m111.3 ft·lb |
| A4-70 | 85.5 kN19226 lbf | 322.4 N·m237.8 ft·lb | 236.6 N·m174.5 ft·lb | 150.9 N·m111.3 ft·lb |
| A4-80 | 114.0 kN25635 lbf | 429.8 N·m317.0 ft·lb | 315.5 N·m232.7 ft·lb | 201.2 N·m148.4 ft·lb |
Torque for M20 hex head bolts and nuts, standard ISO/ASME heads on steel with a 22.0 mm clearance hole. Friction μ applies to both the threads and the bearing face. Always follow the manufacturer's value where one exists.
M20 thread and dimensions
- Coarse thread
- M20×2.5 — pitch 2.5 mm
- Fine thread
- M20×1.5 — pitch 1.5 mm
- Tensile stress area Aₛ
- 244.8 mm² (coarse), 271.5 mm² (fine)
- Pitch diameter d₂
- 18.376 mm
- Tap drill
- 17.5 mm (coarse), 18.5 mm (fine)
- Wrench size (hex head)
- 30 mm
- Clearance hole
- 22.0 mm
How the M20 torque is calculated
Preload is 70% of the bolt's yield strength times its tensile stress area. Torque then follows the ISO 16047 / VDI 2230 formula, which splits it into thread pitch, thread friction and friction under the head:
F = 70% × 640 MPa × 244.8 mm² = 109.7 kN
T = F × (0.16·P + 0.58·μ·d₂ + μ·Dₖₘ/2)
T = 109.7 kN × (0.16·2.5 + 0.58·0.15·18.38 + 0.15·26.00/2) mm = 424.9 N·m
Here d₂ is the pitch diameter and Dₖₘ the effective bearing diameter of the head (26.00 mm). Change the grade, lubrication or preload in the calculator below.
Frequently asked questions
What is the torque for an M20 8.8 bolt?
About 424.9 N·m (313.4 ft·lb) with dry threads, 316.6 N·m (233.5 ft·lb) with oiled threads and 208.4 N·m (153.7 ft·lb) with PTFE or moly paste, for a coarse M20×2.5 thread tightened to 70% of yield. The resulting clamp force is 109.7 kN.
What is the torque for an M20 10.9 bolt?
About 597.5 N·m (440.7 ft·lb) with dry threads, 445.3 N·m (328.4 ft·lb) with oiled threads and 293.1 N·m (216.1 ft·lb) with PTFE or moly paste, for a coarse M20×2.5 thread tightened to 70% of yield. The resulting clamp force is 154.2 kN.
What size wrench fits an M20 bolt?
A standard M20 hex head bolt or nut takes a 30 mm wrench or socket.
What drill size do I need to tap M20?
Use a 17.5 mm drill for M20×2.5 and 18.5 mm for M20×1.5.