3/8" Bolt Torque
A 3/8" Grade 5 bolt with a coarse 3/8"-16 UNC thread needs about 30.8 ft·lb (41.7 N·m) when dry and 23.2 ft·lb (31.5 N·m) when oiled, tightened to 70% of yield (clamp force 22.2 kN).
| Grade | Clamp forcepreload | Dryμ 0.15 | Oiledμ 0.11 | PTFE / moly pasteμ 0.06 |
|---|---|---|---|---|
| Grade 2 | 13.8 kN3092 lbf | 19.1 ft·lb25.9 N·m | 14.4 ft·lb19.5 N·m | 9.70 ft·lb13.2 N·m |
| Grade 5 | 22.2 kN4988 lbf | 30.8 ft·lb41.7 N·m | 23.2 ft·lb31.5 N·m | 15.7 ft·lb21.2 N·m |
| Grade 8 | 31.4 kN7049 lbf | 43.5 ft·lb59.0 N·m | 32.8 ft·lb44.5 N·m | 22.1 ft·lb30.0 N·m |
| A307 | 8.75 kN1967 lbf | 12.1 ft·lb16.5 N·m | 9.15 ft·lb12.4 N·m | 6.17 ft·lb8.37 N·m |
| A574 | 36.2 kN8135 lbf | 50.2 ft·lb68.1 N·m | 37.9 ft·lb51.3 N·m | 25.5 ft·lb34.6 N·m |
| Grade | Clamp forcepreload | Dryμ 0.15 | Oiledμ 0.11 | PTFE / moly pasteμ 0.06 |
|---|---|---|---|---|
| Grade 2 | 15.6 kN3504 lbf | 21.0 ft·lb28.5 N·m | 15.6 ft·lb21.1 N·m | 10.2 ft·lb13.8 N·m |
| Grade 5 | 25.1 kN5653 lbf | 33.9 ft·lb45.9 N·m | 25.1 ft·lb34.1 N·m | 16.4 ft·lb22.2 N·m |
| Grade 8 | 35.5 kN7990 lbf | 47.8 ft·lb64.9 N·m | 35.5 ft·lb48.2 N·m | 23.2 ft·lb31.4 N·m |
| A307 | 9.92 kN2229 lbf | 13.4 ft·lb18.1 N·m | 9.91 ft·lb13.4 N·m | 6.47 ft·lb8.77 N·m |
| A574 | 41.0 kN9220 lbf | 55.2 ft·lb74.9 N·m | 41.0 ft·lb55.6 N·m | 26.8 ft·lb36.3 N·m |
Torque for 3/8" hex head bolts and nuts, standard ISO/ASME heads on steel with a 10.3 mm clearance hole. Friction μ applies to both the threads and the bearing face. Always follow the manufacturer's value where one exists.
3/8" thread and dimensions
- Coarse thread
- 3/8"-16 UNC — pitch 16 TPI
- Fine thread
- 3/8"-24 UNF — pitch 24 TPI
- Tensile stress area Aₛ
- 50.0 mm² (coarse), 56.7 mm² (fine)
- Pitch diameter d₂
- 8.494 mm
- Tap drill
- 5/16 (coarse), Q (fine)
- Wrench size (hex head)
- 9/16"
- Clearance hole
- 10.3 mm
How the 3/8" 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% × 634 MPa × 50.0 mm² = 22.2 kN
T = F × (0.16·P + 0.58·μ·d₂ + μ·Dₖₘ/2)
T = 22.2 kN × (0.16·1.59 + 0.58·0.15·8.49 + 0.15·12.30/2) mm = 41.7 N·m
Here d₂ is the pitch diameter and Dₖₘ the effective bearing diameter of the head (12.30 mm). Change the grade, lubrication or preload in the calculator below.
Frequently asked questions
What is the torque for a 3/8" Grade 5 bolt?
About 30.8 ft·lb (41.7 N·m) with dry threads, 23.2 ft·lb (31.5 N·m) with oiled threads and 15.7 ft·lb (21.2 N·m) with PTFE or moly paste, for a coarse 3/8"-16 UNC thread tightened to 70% of yield. The resulting clamp force is 22.2 kN.
What is the torque for a 3/8" Grade 8 bolt?
About 43.5 ft·lb (59.0 N·m) with dry threads, 32.8 ft·lb (44.5 N·m) with oiled threads and 22.1 ft·lb (30.0 N·m) with PTFE or moly paste, for a coarse 3/8"-16 UNC thread tightened to 70% of yield. The resulting clamp force is 31.4 kN.
What size wrench fits a 3/8" bolt?
A standard 3/8" hex head bolt or nut takes a 9/16" wrench or socket.
What drill size do I need to tap 3/8"?
Use a 5/16 drill for 3/8"-16 UNC and Q for 3/8"-24 UNF.