5/16" Bolt Torque
A 5/16" Grade 5 bolt with a coarse 5/16"-18 UNC thread needs about 17.8 ft·lb (24.2 N·m) when dry and 13.5 ft·lb (18.3 N·m) when oiled, tightened to 70% of yield (clamp force 15.0 kN).
| Grade | Clamp forcepreload | Dryμ 0.15 | Oiledμ 0.11 | PTFE / moly pasteμ 0.06 |
|---|---|---|---|---|
| Grade 2 | 9.31 kN2092 lbf | 11.1 ft·lb15.0 N·m | 8.35 ft·lb11.3 N·m | 5.65 ft·lb7.67 N·m |
| Grade 5 | 15.0 kN3375 lbf | 17.8 ft·lb24.2 N·m | 13.5 ft·lb18.3 N·m | 9.12 ft·lb12.4 N·m |
| Grade 8 | 21.2 kN4769 lbf | 25.2 ft·lb34.2 N·m | 19.0 ft·lb25.8 N·m | 12.9 ft·lb17.5 N·m |
| A307 | 5.92 kN1331 lbf | 7.03 ft·lb9.53 N·m | 5.31 ft·lb7.21 N·m | 3.60 ft·lb4.88 N·m |
| A574 | 24.5 kN5504 lbf | 29.1 ft·lb39.4 N·m | 22.0 ft·lb29.8 N·m | 14.9 ft·lb20.2 N·m |
| Grade | Clamp forcepreload | Dryμ 0.15 | Oiledμ 0.11 | PTFE / moly pasteμ 0.06 |
|---|---|---|---|---|
| Grade 2 | 10.3 kN2317 lbf | 12.0 ft·lb16.2 N·m | 8.93 ft·lb12.1 N·m | 5.90 ft·lb7.99 N·m |
| Grade 5 | 16.6 kN3738 lbf | 19.3 ft·lb26.2 N·m | 14.4 ft·lb19.5 N·m | 9.51 ft·lb12.9 N·m |
| Grade 8 | 23.5 kN5282 lbf | 27.3 ft·lb37.0 N·m | 20.4 ft·lb27.6 N·m | 13.4 ft·lb18.2 N·m |
| A307 | 6.56 kN1474 lbf | 7.61 ft·lb10.3 N·m | 5.68 ft·lb7.70 N·m | 3.75 ft·lb5.09 N·m |
| A574 | 27.1 kN6096 lbf | 31.5 ft·lb42.7 N·m | 23.5 ft·lb31.9 N·m | 15.5 ft·lb21.0 N·m |
Torque for 5/16" hex head bolts and nuts, standard ISO/ASME heads on steel with a 8.7 mm clearance hole. Friction μ applies to both the threads and the bearing face. Always follow the manufacturer's value where one exists.
5/16" thread and dimensions
- Coarse thread
- 5/16"-18 UNC — pitch 18 TPI
- Fine thread
- 5/16"-24 UNF — pitch 24 TPI
- Tensile stress area Aₛ
- 33.8 mm² (coarse), 37.5 mm² (fine)
- Pitch diameter d₂
- 7.021 mm
- Tap drill
- F (coarse), I (fine)
- Wrench size (hex head)
- 1/2"
- Clearance hole
- 8.7 mm
How the 5/16" 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 × 33.8 mm² = 15.0 kN
T = F × (0.16·P + 0.58·μ·d₂ + μ·Dₖₘ/2)
T = 15.0 kN × (0.16·1.41 + 0.58·0.15·7.02 + 0.15·10.72/2) mm = 24.2 N·m
Here d₂ is the pitch diameter and Dₖₘ the effective bearing diameter of the head (10.72 mm). Change the grade, lubrication or preload in the calculator below.
Frequently asked questions
What is the torque for a 5/16" Grade 5 bolt?
About 17.8 ft·lb (24.2 N·m) with dry threads, 13.5 ft·lb (18.3 N·m) with oiled threads and 9.12 ft·lb (12.4 N·m) with PTFE or moly paste, for a coarse 5/16"-18 UNC thread tightened to 70% of yield. The resulting clamp force is 15.0 kN.
What is the torque for a 5/16" Grade 8 bolt?
About 25.2 ft·lb (34.2 N·m) with dry threads, 19.0 ft·lb (25.8 N·m) with oiled threads and 12.9 ft·lb (17.5 N·m) with PTFE or moly paste, for a coarse 5/16"-18 UNC thread tightened to 70% of yield. The resulting clamp force is 21.2 kN.
What size wrench fits a 5/16" bolt?
A standard 5/16" hex head bolt or nut takes a 1/2" wrench or socket.
What drill size do I need to tap 5/16"?
Use a F drill for 5/16"-18 UNC and I for 5/16"-24 UNF.