M39 Bolt Torque
An M39 8.8 bolt with a coarse M39×4 thread needs about 3272.1 N·m (2413.3 ft·lb) when dry and 2422.0 N·m (1786.4 ft·lb) when oiled, tightened to 70% of yield (clamp force 437.1 kN).
| Grade | Clamp forcepreload | Dryμ 0.15 | Oiledμ 0.11 | PTFE / moly pasteμ 0.06 |
|---|---|---|---|---|
| 4.6 | 163.9 kN36852 lbf | 1227.0 N·m905.0 ft·lb | 908.2 N·m669.9 ft·lb | 589.5 N·m434.8 ft·lb |
| 4.8 | 218.6 kN49136 lbf | 1636.0 N·m1206.7 ft·lb | 1211.0 N·m893.2 ft·lb | 785.9 N·m579.7 ft·lb |
| 5.6 | 204.9 kN46065 lbf | 1533.8 N·m1131.3 ft·lb | 1135.3 N·m837.4 ft·lb | 736.8 N·m543.5 ft·lb |
| 5.8 | 273.2 kN61420 lbf | 2045.0 N·m1508.3 ft·lb | 1513.7 N·m1116.5 ft·lb | 982.4 N·m724.6 ft·lb |
| 6.8 | 327.9 kN73704 lbf | 2454.0 N·m1810.0 ft·lb | 1816.5 N·m1339.8 ft·lb | 1178.9 N·m869.5 ft·lb |
| 8.8 | 437.1 kN98272 lbf | 3272.1 N·m2413.3 ft·lb | 2422.0 N·m1786.4 ft·lb | 1571.9 N·m1159.4 ft·lb |
| 10.9 | 614.7 kN138195 lbf | 4601.3 N·m3393.8 ft·lb | 3405.9 N·m2512.1 ft·lb | 2210.5 N·m1630.4 ft·lb |
| 12.9 | 737.7 kN165834 lbf | 5521.6 N·m4072.5 ft·lb | 4087.1 N·m3014.5 ft·lb | 2652.6 N·m1956.4 ft·lb |
| A2-70 | 307.4 kN69098 lbf | 2300.7 N·m1696.9 ft·lb | 1702.9 N·m1256.0 ft·lb | 1105.2 N·m815.2 ft·lb |
| A4-70 | 307.4 kN69098 lbf | 2300.7 N·m1696.9 ft·lb | 1702.9 N·m1256.0 ft·lb | 1105.2 N·m815.2 ft·lb |
| A4-80 | 409.8 kN92130 lbf | 3067.5 N·m2262.5 ft·lb | 2270.6 N·m1674.7 ft·lb | 1473.6 N·m1086.9 ft·lb |
| Grade | Clamp forcepreload | Dryμ 0.15 | Oiledμ 0.11 | PTFE / moly pasteμ 0.06 |
|---|---|---|---|---|
| 4.6 | 172.8 kN38840 lbf | 1275.1 N·m940.5 ft·lb | 936.4 N·m690.7 ft·lb | 597.7 N·m440.9 ft·lb |
| 4.8 | 230.4 kN51787 lbf | 1700.2 N·m1254.0 ft·lb | 1248.6 N·m920.9 ft·lb | 797.0 N·m587.8 ft·lb |
| 5.6 | 216.0 kN48550 lbf | 1593.9 N·m1175.6 ft·lb | 1170.5 N·m863.3 ft·lb | 747.2 N·m551.1 ft·lb |
| 5.8 | 287.9 kN64733 lbf | 2125.2 N·m1567.5 ft·lb | 1560.7 N·m1151.1 ft·lb | 996.2 N·m734.8 ft·lb |
| 6.8 | 345.5 kN77680 lbf | 2550.2 N·m1881.0 ft·lb | 1872.9 N·m1381.4 ft·lb | 1195.5 N·m881.7 ft·lb |
| 8.8 | 460.7 kN103573 lbf | 3400.3 N·m2508.0 ft·lb | 2497.2 N·m1841.8 ft·lb | 1594.0 N·m1175.7 ft·lb |
| 10.9 | 647.9 kN145650 lbf | 4781.7 N·m3526.8 ft·lb | 3511.6 N·m2590.0 ft·lb | 2241.5 N·m1653.3 ft·lb |
| 12.9 | 777.5 kN174780 lbf | 5738.1 N·m4232.2 ft·lb | 4213.9 N·m3108.0 ft·lb | 2689.8 N·m1983.9 ft·lb |
| A2-70 | 323.9 kN72825 lbf | 2390.9 N·m1763.4 ft·lb | 1755.8 N·m1295.0 ft·lb | 1120.8 N·m826.6 ft·lb |
| A4-70 | 323.9 kN72825 lbf | 2390.9 N·m1763.4 ft·lb | 1755.8 N·m1295.0 ft·lb | 1120.8 N·m826.6 ft·lb |
| A4-80 | 431.9 kN97100 lbf | 3187.8 N·m2351.2 ft·lb | 2341.1 N·m1726.7 ft·lb | 1494.4 N·m1102.2 ft·lb |
Torque for M39 hex head bolts and nuts, standard ISO/ASME heads on steel with a 42.0 mm clearance hole. Friction μ applies to both the threads and the bearing face. Always follow the manufacturer's value where one exists.
M39 thread and dimensions
- Coarse thread
- M39×4 — pitch 4 mm
- Fine thread
- M39×3 — pitch 3 mm
- Tensile stress area Aₛ
- 975.8 mm² (coarse), 1028.4 mm² (fine)
- Pitch diameter d₂
- 36.402 mm
- Tap drill
- 35 mm (coarse), 36 mm (fine)
- Wrench size (hex head)
- 60 mm
- Clearance hole
- 42.0 mm
How the M39 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 × 975.8 mm² = 437.1 kN
T = F × (0.16·P + 0.58·μ·d₂ + μ·Dₖₘ/2)
T = 437.1 kN × (0.16·4 + 0.58·0.15·36.40 + 0.15·51.00/2) mm = 3272.1 N·m
Here d₂ is the pitch diameter and Dₖₘ the effective bearing diameter of the head (51.00 mm). Change the grade, lubrication or preload in the calculator below.
Frequently asked questions
What is the torque for an M39 8.8 bolt?
About 3272.1 N·m (2413.3 ft·lb) with dry threads, 2422.0 N·m (1786.4 ft·lb) with oiled threads and 1571.9 N·m (1159.4 ft·lb) with PTFE or moly paste, for a coarse M39×4 thread tightened to 70% of yield. The resulting clamp force is 437.1 kN.
What is the torque for an M39 10.9 bolt?
About 4601.3 N·m (3393.8 ft·lb) with dry threads, 3405.9 N·m (2512.1 ft·lb) with oiled threads and 2210.5 N·m (1630.4 ft·lb) with PTFE or moly paste, for a coarse M39×4 thread tightened to 70% of yield. The resulting clamp force is 614.7 kN.
What size wrench fits an M39 bolt?
A standard M39 hex head bolt or nut takes a 60 mm wrench or socket.
What drill size do I need to tap M39?
Use a 35 mm drill for M39×4 and 36 mm for M39×3.