M8 Bolt Torque
An M8 8.8 bolt with a coarse M8×1.25 thread needs about 26.6 N·m (19.6 ft·lb) when dry and 20.0 N·m (14.7 ft·lb) when oiled, tightened to 70% of yield (clamp force 16.4 kN).
| Grade | Clamp forcepreload | Dryμ 0.15 | Oiledμ 0.11 | PTFE / moly pasteμ 0.06 |
|---|---|---|---|---|
| 4.6 | 6.15 kN1383 lbf | 9.96 N·m7.35 ft·lb | 7.48 N·m5.52 ft·lb | 5.00 N·m3.69 ft·lb |
| 4.8 | 8.20 kN1843 lbf | 13.3 N·m9.80 ft·lb | 9.98 N·m7.36 ft·lb | 6.67 N·m4.92 ft·lb |
| 5.6 | 7.69 kN1728 lbf | 12.5 N·m9.19 ft·lb | 9.35 N·m6.90 ft·lb | 6.25 N·m4.61 ft·lb |
| 5.8 | 10.3 kN2304 lbf | 16.6 N·m12.2 ft·lb | 12.5 N·m9.20 ft·lb | 8.34 N·m6.15 ft·lb |
| 6.8 | 12.3 kN2765 lbf | 19.9 N·m14.7 ft·lb | 15.0 N·m11.0 ft·lb | 10.0 N·m7.38 ft·lb |
| 8.8 | 16.4 kN3687 lbf | 26.6 N·m19.6 ft·lb | 20.0 N·m14.7 ft·lb | 13.3 N·m9.84 ft·lb |
| 9.8 | 18.5 kN4148 lbf | 29.9 N·m22.0 ft·lb | 22.4 N·m16.6 ft·lb | 15.0 N·m11.1 ft·lb |
| 10.9 | 23.1 kN5185 lbf | 37.4 N·m27.6 ft·lb | 28.1 N·m20.7 ft·lb | 18.8 N·m13.8 ft·lb |
| 12.9 | 27.7 kN6222 lbf | 44.8 N·m33.1 ft·lb | 33.7 N·m24.8 ft·lb | 22.5 N·m16.6 ft·lb |
| A2-70 | 11.5 kN2592 lbf | 18.7 N·m13.8 ft·lb | 14.0 N·m10.3 ft·lb | 9.38 N·m6.92 ft·lb |
| A4-70 | 11.5 kN2592 lbf | 18.7 N·m13.8 ft·lb | 14.0 N·m10.3 ft·lb | 9.38 N·m6.92 ft·lb |
| A4-80 | 15.4 kN3457 lbf | 24.9 N·m18.4 ft·lb | 18.7 N·m13.8 ft·lb | 12.5 N·m9.22 ft·lb |
| Grade | Clamp forcepreload | Dryμ 0.15 | Oiledμ 0.11 | PTFE / moly pasteμ 0.06 |
|---|---|---|---|---|
| 4.6 | 6.58 kN1479 lbf | 10.5 N·m7.73 ft·lb | 7.81 N·m5.76 ft·lb | 5.13 N·m3.78 ft·lb |
| 4.8 | 8.77 kN1972 lbf | 14.0 N·m10.3 ft·lb | 10.4 N·m7.68 ft·lb | 6.84 N·m5.04 ft·lb |
| 5.6 | 8.23 kN1849 lbf | 13.1 N·m9.67 ft·lb | 9.76 N·m7.20 ft·lb | 6.41 N·m4.73 ft·lb |
| 5.8 | 11.0 kN2465 lbf | 17.5 N·m12.9 ft·lb | 13.0 N·m9.60 ft·lb | 8.54 N·m6.30 ft·lb |
| 6.8 | 13.2 kN2959 lbf | 21.0 N·m15.5 ft·lb | 15.6 N·m11.5 ft·lb | 10.3 N·m7.56 ft·lb |
| 8.8 | 17.5 kN3945 lbf | 28.0 N·m20.6 ft·lb | 20.8 N·m15.4 ft·lb | 13.7 N·m10.1 ft·lb |
| 9.8 | 19.7 kN4438 lbf | 31.5 N·m23.2 ft·lb | 23.4 N·m17.3 ft·lb | 15.4 N·m11.3 ft·lb |
| 10.9 | 24.7 kN5547 lbf | 39.3 N·m29.0 ft·lb | 29.3 N·m21.6 ft·lb | 19.2 N·m14.2 ft·lb |
| 12.9 | 29.6 kN6657 lbf | 47.2 N·m34.8 ft·lb | 35.1 N·m25.9 ft·lb | 23.1 N·m17.0 ft·lb |
| A2-70 | 12.3 kN2774 lbf | 19.7 N·m14.5 ft·lb | 14.6 N·m10.8 ft·lb | 9.61 N·m7.09 ft·lb |
| A4-70 | 12.3 kN2774 lbf | 19.7 N·m14.5 ft·lb | 14.6 N·m10.8 ft·lb | 9.61 N·m7.09 ft·lb |
| A4-80 | 16.5 kN3698 lbf | 26.2 N·m19.3 ft·lb | 19.5 N·m14.4 ft·lb | 12.8 N·m9.45 ft·lb |
Torque for M8 hex head bolts and nuts, standard ISO/ASME heads on steel with a 9.0 mm clearance hole. Friction μ applies to both the threads and the bearing face. Always follow the manufacturer's value where one exists.
M8 thread and dimensions
- Coarse thread
- M8×1.25 — pitch 1.25 mm
- Fine thread
- M8×1 — pitch 1 mm
- Tensile stress area Aₛ
- 36.6 mm² (coarse), 39.2 mm² (fine)
- Pitch diameter d₂
- 7.188 mm
- Tap drill
- 6.8 mm (coarse), 7 mm (fine)
- Wrench size (hex head)
- 13 mm
- Clearance hole
- 9.0 mm
How the M8 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 × 36.6 mm² = 16.4 kN
T = F × (0.16·P + 0.58·μ·d₂ + μ·Dₖₘ/2)
T = 16.4 kN × (0.16·1.25 + 0.58·0.15·7.19 + 0.15·11.00/2) mm = 26.6 N·m
Here d₂ is the pitch diameter and Dₖₘ the effective bearing diameter of the head (11.00 mm). Change the grade, lubrication or preload in the calculator below.
Frequently asked questions
What is the torque for an M8 8.8 bolt?
About 26.6 N·m (19.6 ft·lb) with dry threads, 20.0 N·m (14.7 ft·lb) with oiled threads and 13.3 N·m (9.84 ft·lb) with PTFE or moly paste, for a coarse M8×1.25 thread tightened to 70% of yield. The resulting clamp force is 16.4 kN.
What is the torque for an M8 10.9 bolt?
About 37.4 N·m (27.6 ft·lb) with dry threads, 28.1 N·m (20.7 ft·lb) with oiled threads and 18.8 N·m (13.8 ft·lb) with PTFE or moly paste, for a coarse M8×1.25 thread tightened to 70% of yield. The resulting clamp force is 23.1 kN.
What size wrench fits an M8 bolt?
A standard M8 hex head bolt or nut takes a 13 mm wrench or socket.
What drill size do I need to tap M8?
Use a 6.8 mm drill for M8×1.25 and 7 mm for M8×1.