1/2" Bolt Torque
A 1/2" Grade 5 bolt with a coarse 1/2"-13 UNC thread needs about 75.2 ft·lb (102.0 N·m) when dry and 56.5 ft·lb (76.6 N·m) when oiled, tightened to 70% of yield (clamp force 40.6 kN).
| Grade | Clamp forcepreload | Dryμ 0.15 | Oiledμ 0.11 | PTFE / moly pasteμ 0.06 |
|---|---|---|---|---|
| Grade 2 | 25.2 kN5662 lbf | 46.6 ft·lb63.2 N·m | 35.0 ft·lb47.5 N·m | 23.4 ft·lb31.8 N·m |
| Grade 5 | 40.6 kN9134 lbf | 75.2 ft·lb102.0 N·m | 56.5 ft·lb76.6 N·m | 37.8 ft·lb51.3 N·m |
| Grade 8 | 57.4 kN12908 lbf | 106.3 ft·lb144.1 N·m | 79.9 ft·lb108.3 N·m | 53.4 ft·lb72.4 N·m |
| A307 | 16.0 kN3602 lbf | 29.7 ft·lb40.2 N·m | 22.3 ft·lb30.2 N·m | 14.9 ft·lb20.2 N·m |
| A325 | 40.6 kN9134 lbf | 75.2 ft·lb102.0 N·m | 56.5 ft·lb76.6 N·m | 37.8 ft·lb51.3 N·m |
| A490 | 57.4 kN12908 lbf | 106.3 ft·lb144.1 N·m | 79.9 ft·lb108.3 N·m | 53.4 ft·lb72.4 N·m |
| A574 | 66.3 kN14896 lbf | 122.7 ft·lb166.3 N·m | 92.2 ft·lb125.0 N·m | 61.7 ft·lb83.6 N·m |
| Grade | Clamp forcepreload | Dryμ 0.15 | Oiledμ 0.11 | PTFE / moly pasteμ 0.06 |
|---|---|---|---|---|
| Grade 2 | 28.4 kN6382 lbf | 51.1 ft·lb69.2 N·m | 37.8 ft·lb51.2 N·m | 24.5 ft·lb33.2 N·m |
| Grade 5 | 45.8 kN10296 lbf | 82.4 ft·lb111.7 N·m | 60.9 ft·lb82.6 N·m | 39.5 ft·lb53.5 N·m |
| Grade 8 | 64.7 kN14551 lbf | 116.4 ft·lb157.8 N·m | 86.1 ft·lb116.7 N·m | 55.8 ft·lb75.6 N·m |
| A307 | 18.1 kN4060 lbf | 32.5 ft·lb44.0 N·m | 24.0 ft·lb32.6 N·m | 15.6 ft·lb21.1 N·m |
| A325 | 45.8 kN10296 lbf | 82.4 ft·lb111.7 N·m | 60.9 ft·lb82.6 N·m | 39.5 ft·lb53.5 N·m |
| A490 | 64.7 kN14551 lbf | 116.4 ft·lb157.8 N·m | 86.1 ft·lb116.7 N·m | 55.8 ft·lb75.6 N·m |
| A574 | 74.7 kN16792 lbf | 134.3 ft·lb182.1 N·m | 99.4 ft·lb134.7 N·m | 64.4 ft·lb87.3 N·m |
Torque for 1/2" hex head bolts and nuts, standard ISO/ASME heads on steel with a 14.3 mm clearance hole. Friction μ applies to both the threads and the bearing face. Always follow the manufacturer's value where one exists.
1/2" thread and dimensions
- Coarse thread
- 1/2"-13 UNC — pitch 13 TPI
- Fine thread
- 1/2"-20 UNF — pitch 20 TPI
- Tensile stress area Aₛ
- 91.5 mm² (coarse), 103.2 mm² (fine)
- Pitch diameter d₂
- 11.431 mm
- Tap drill
- 27/64 (coarse), 29/64 (fine)
- Wrench size (hex head)
- 3/4"
- Clearance hole
- 14.3 mm
How the 1/2" 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 × 91.5 mm² = 40.6 kN
T = F × (0.16·P + 0.58·μ·d₂ + μ·Dₖₘ/2)
T = 40.6 kN × (0.16·1.95 + 0.58·0.15·11.43 + 0.15·16.67/2) mm = 102.0 N·m
Here d₂ is the pitch diameter and Dₖₘ the effective bearing diameter of the head (16.67 mm). Change the grade, lubrication or preload in the calculator below.
Frequently asked questions
What is the torque for a 1/2" Grade 5 bolt?
About 75.2 ft·lb (102.0 N·m) with dry threads, 56.5 ft·lb (76.6 N·m) with oiled threads and 37.8 ft·lb (51.3 N·m) with PTFE or moly paste, for a coarse 1/2"-13 UNC thread tightened to 70% of yield. The resulting clamp force is 40.6 kN.
What is the torque for a 1/2" Grade 8 bolt?
About 106.3 ft·lb (144.1 N·m) with dry threads, 79.9 ft·lb (108.3 N·m) with oiled threads and 53.4 ft·lb (72.4 N·m) with PTFE or moly paste, for a coarse 1/2"-13 UNC thread tightened to 70% of yield. The resulting clamp force is 57.4 kN.
What size wrench fits a 1/2" bolt?
A standard 1/2" hex head bolt or nut takes a 3/4" wrench or socket.
What drill size do I need to tap 1/2"?
Use a 27/64 drill for 1/2"-13 UNC and 29/64 for 1/2"-20 UNF.