M3 Bolt Torque
An M3 8.8 bolt with a coarse M3×0.5 thread needs about 1.43 N·m (1.05 ft·lb) when dry and 1.08 N·m (0.79 ft·lb) when oiled, tightened to 70% of yield (clamp force 2.25 kN).
| Grade | Clamp forcepreload | Dryμ 0.15 | Oiledμ 0.11 | PTFE / moly pasteμ 0.06 |
|---|---|---|---|---|
| 4.6 | 0.85 kN190 lbf | 0.54 N·m0.40 ft·lb | 0.40 N·m0.30 ft·lb | 0.27 N·m0.20 ft·lb |
| 4.8 | 1.13 kN253 lbf | 0.72 N·m0.53 ft·lb | 0.54 N·m0.40 ft·lb | 0.36 N·m0.27 ft·lb |
| 5.6 | 1.06 kN238 lbf | 0.67 N·m0.49 ft·lb | 0.50 N·m0.37 ft·lb | 0.34 N·m0.25 ft·lb |
| 5.8 | 1.41 kN317 lbf | 0.89 N·m0.66 ft·lb | 0.67 N·m0.50 ft·lb | 0.45 N·m0.33 ft·lb |
| 6.8 | 1.69 kN380 lbf | 1.07 N·m0.79 ft·lb | 0.81 N·m0.59 ft·lb | 0.54 N·m0.40 ft·lb |
| 8.8 | 2.25 kN507 lbf | 1.43 N·m1.05 ft·lb | 1.08 N·m0.79 ft·lb | 0.72 N·m0.53 ft·lb |
| 9.8 | 2.54 kN570 lbf | 1.61 N·m1.19 ft·lb | 1.21 N·m0.89 ft·lb | 0.81 N·m0.60 ft·lb |
| 10.9 | 3.17 kN713 lbf | 2.01 N·m1.48 ft·lb | 1.51 N·m1.12 ft·lb | 1.01 N·m0.75 ft·lb |
| 12.9 | 3.80 kN855 lbf | 2.41 N·m1.78 ft·lb | 1.81 N·m1.34 ft·lb | 1.22 N·m0.90 ft·lb |
| A2-70 | 1.58 kN356 lbf | 1.01 N·m0.74 ft·lb | 0.76 N·m0.56 ft·lb | 0.51 N·m0.37 ft·lb |
| A4-70 | 1.58 kN356 lbf | 1.01 N·m0.74 ft·lb | 0.76 N·m0.56 ft·lb | 0.51 N·m0.37 ft·lb |
| A4-80 | 2.11 kN475 lbf | 1.34 N·m0.99 ft·lb | 1.01 N·m0.74 ft·lb | 0.68 N·m0.50 ft·lb |
| Grade | Clamp forcepreload | Dryμ 0.15 | Oiledμ 0.11 | PTFE / moly pasteμ 0.06 |
|---|---|---|---|---|
| 4.6 | 0.94 kN212 lbf | 0.58 N·m0.43 ft·lb | 0.43 N·m0.32 ft·lb | 0.28 N·m0.21 ft·lb |
| 4.8 | 1.26 kN282 lbf | 0.78 N·m0.57 ft·lb | 0.58 N·m0.43 ft·lb | 0.38 N·m0.28 ft·lb |
| 5.6 | 1.18 kN265 lbf | 0.73 N·m0.54 ft·lb | 0.54 N·m0.40 ft·lb | 0.35 N·m0.26 ft·lb |
| 5.8 | 1.57 kN353 lbf | 0.97 N·m0.72 ft·lb | 0.72 N·m0.53 ft·lb | 0.47 N·m0.35 ft·lb |
| 6.8 | 1.88 kN423 lbf | 1.17 N·m0.86 ft·lb | 0.86 N·m0.64 ft·lb | 0.56 N·m0.42 ft·lb |
| 8.8 | 2.51 kN565 lbf | 1.55 N·m1.15 ft·lb | 1.15 N·m0.85 ft·lb | 0.75 N·m0.55 ft·lb |
| 9.8 | 2.83 kN635 lbf | 1.75 N·m1.29 ft·lb | 1.30 N·m0.96 ft·lb | 0.84 N·m0.62 ft·lb |
| 10.9 | 3.53 kN794 lbf | 2.19 N·m1.61 ft·lb | 1.62 N·m1.20 ft·lb | 1.06 N·m0.78 ft·lb |
| 12.9 | 4.24 kN953 lbf | 2.62 N·m1.93 ft·lb | 1.95 N·m1.43 ft·lb | 1.27 N·m0.93 ft·lb |
| A2-70 | 1.77 kN397 lbf | 1.09 N·m0.81 ft·lb | 0.81 N·m0.60 ft·lb | 0.53 N·m0.39 ft·lb |
| A4-70 | 1.77 kN397 lbf | 1.09 N·m0.81 ft·lb | 0.81 N·m0.60 ft·lb | 0.53 N·m0.39 ft·lb |
| A4-80 | 2.35 kN529 lbf | 1.46 N·m1.07 ft·lb | 1.08 N·m0.80 ft·lb | 0.70 N·m0.52 ft·lb |
Torque for M3 hex head bolts and nuts, standard ISO/ASME heads on steel with a 3.4 mm clearance hole. Friction μ applies to both the threads and the bearing face. Always follow the manufacturer's value where one exists.
M3 thread and dimensions
- Coarse thread
- M3×0.5 — pitch 0.5 mm
- Fine thread
- M3×0.35 — pitch 0.35 mm
- Tensile stress area Aₛ
- 5.03 mm² (coarse), 5.61 mm² (fine)
- Pitch diameter d₂
- 2.675 mm
- Tap drill
- 2.5 mm (coarse), 2.65 mm (fine)
- Wrench size (hex head)
- 5.5 mm
- Clearance hole
- 3.4 mm
How the M3 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 × 5.03 mm² = 2.25 kN
T = F × (0.16·P + 0.58·μ·d₂ + μ·Dₖₘ/2)
T = 2.25 kN × (0.16·0.5 + 0.58·0.15·2.68 + 0.15·4.45/2) mm = 1.43 N·m
Here d₂ is the pitch diameter and Dₖₘ the effective bearing diameter of the head (4.45 mm). Change the grade, lubrication or preload in the calculator below.
Frequently asked questions
What is the torque for an M3 8.8 bolt?
About 1.43 N·m (1.05 ft·lb) with dry threads, 1.08 N·m (0.79 ft·lb) with oiled threads and 0.72 N·m (0.53 ft·lb) with PTFE or moly paste, for a coarse M3×0.5 thread tightened to 70% of yield. The resulting clamp force is 2.25 kN.
What is the torque for an M3 10.9 bolt?
About 2.01 N·m (1.48 ft·lb) with dry threads, 1.51 N·m (1.12 ft·lb) with oiled threads and 1.01 N·m (0.75 ft·lb) with PTFE or moly paste, for a coarse M3×0.5 thread tightened to 70% of yield. The resulting clamp force is 3.17 kN.
What size wrench fits an M3 bolt?
A standard M3 hex head bolt or nut takes a 5.5 mm wrench or socket.
What drill size do I need to tap M3?
Use a 2.5 mm drill for M3×0.5 and 2.65 mm for M3×0.35.