1/4" Bolt Torque
A 1/4" Grade 5 bolt with a coarse 1/4"-20 UNC thread needs about 9.03 ft·lb (12.2 N·m) when dry and 6.85 ft·lb (9.29 N·m) when oiled, tightened to 70% of yield (clamp force 9.11 kN).
| Grade | Clamp forcepreload | Dryμ 0.15 | Oiledμ 0.11 | PTFE / moly pasteμ 0.06 |
|---|---|---|---|---|
| Grade 2 | 5.65 kN1270 lbf | 5.60 ft·lb7.59 N·m | 4.25 ft·lb5.76 N·m | 2.90 ft·lb3.93 N·m |
| Grade 5 | 9.11 kN2048 lbf | 9.03 ft·lb12.2 N·m | 6.85 ft·lb9.29 N·m | 4.68 ft·lb6.34 N·m |
| Grade 8 | 12.9 kN2895 lbf | 12.8 ft·lb17.3 N·m | 9.69 ft·lb13.1 N·m | 6.61 ft·lb8.96 N·m |
| A307 | 3.59 kN808 lbf | 3.56 ft·lb4.83 N·m | 2.70 ft·lb3.66 N·m | 1.84 ft·lb2.50 N·m |
| A574 | 14.9 kN3341 lbf | 14.7 ft·lb20.0 N·m | 11.2 ft·lb15.2 N·m | 7.63 ft·lb10.3 N·m |
| Grade | Clamp forcepreload | Dryμ 0.15 | Oiledμ 0.11 | PTFE / moly pasteμ 0.06 |
|---|---|---|---|---|
| Grade 2 | 6.46 kN1451 lbf | 6.22 ft·lb8.43 N·m | 4.65 ft·lb6.30 N·m | 3.08 ft·lb4.17 N·m |
| Grade 5 | 10.4 kN2341 lbf | 10.0 ft·lb13.6 N·m | 7.50 ft·lb10.2 N·m | 4.97 ft·lb6.73 N·m |
| Grade 8 | 14.7 kN3309 lbf | 14.2 ft·lb19.2 N·m | 10.6 ft·lb14.4 N·m | 7.02 ft·lb9.51 N·m |
| A307 | 4.11 kN923 lbf | 3.96 ft·lb5.36 N·m | 2.96 ft·lb4.01 N·m | 1.96 ft·lb2.65 N·m |
| A574 | 17.0 kN3818 lbf | 16.4 ft·lb22.2 N·m | 12.2 ft·lb16.6 N·m | 8.10 ft·lb11.0 N·m |
Torque for 1/4" hex head bolts and nuts, standard ISO/ASME heads on steel with a 7.1 mm clearance hole. Friction μ applies to both the threads and the bearing face. Always follow the manufacturer's value where one exists.
1/4" thread and dimensions
- Coarse thread
- 1/4"-20 UNC — pitch 20 TPI
- Fine thread
- 1/4"-28 UNF — pitch 28 TPI
- Tensile stress area Aₛ
- 20.5 mm² (coarse), 23.5 mm² (fine)
- Pitch diameter d₂
- 5.525 mm
- Tap drill
- #7 (coarse), #3 (fine)
- Wrench size (hex head)
- 7/16"
- Clearance hole
- 7.1 mm
How the 1/4" 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 × 20.5 mm² = 9.11 kN
T = F × (0.16·P + 0.58·μ·d₂ + μ·Dₖₘ/2)
T = 9.11 kN × (0.16·1.27 + 0.58·0.15·5.53 + 0.15·9.13/2) mm = 12.2 N·m
Here d₂ is the pitch diameter and Dₖₘ the effective bearing diameter of the head (9.13 mm). Change the grade, lubrication or preload in the calculator below.
Frequently asked questions
What is the torque for a 1/4" Grade 5 bolt?
About 9.03 ft·lb (12.2 N·m) with dry threads, 6.85 ft·lb (9.29 N·m) with oiled threads and 4.68 ft·lb (6.34 N·m) with PTFE or moly paste, for a coarse 1/4"-20 UNC thread tightened to 70% of yield. The resulting clamp force is 9.11 kN.
What is the torque for a 1/4" Grade 8 bolt?
About 12.8 ft·lb (17.3 N·m) with dry threads, 9.69 ft·lb (13.1 N·m) with oiled threads and 6.61 ft·lb (8.96 N·m) with PTFE or moly paste, for a coarse 1/4"-20 UNC thread tightened to 70% of yield. The resulting clamp force is 12.9 kN.
What size wrench fits a 1/4" bolt?
A standard 1/4" hex head bolt or nut takes a 7/16" wrench or socket.
What drill size do I need to tap 1/4"?
Use a #7 drill for 1/4"-20 UNC and #3 for 1/4"-28 UNF.