1-3/8" Bolt Torque
A 1-3/8" Grade 5 bolt with a coarse 1-3/8"-6 UNC thread needs about 1434.2 ft·lb (1944.5 N·m) when dry and 1068.1 ft·lb (1448.1 N·m) when oiled, tightened to 70% of yield (clamp force 291.0 kN).
| Grade | Clamp forcepreload | Dryμ 0.15 | Oiledμ 0.11 | PTFE / moly pasteμ 0.06 |
|---|---|---|---|---|
| Grade 2 | 129.3 kN29078 lbf | 637.4 ft·lb864.2 N·m | 474.7 ft·lb643.6 N·m | 312.0 ft·lb423.0 N·m |
| Grade 5 | 291.0 kN65426 lbf | 1434.2 ft·lb1944.5 N·m | 1068.1 ft·lb1448.1 N·m | 701.9 ft·lb951.7 N·m |
| Grade 8 | 467.3 kN105057 lbf | 2303.0 ft·lb3122.4 N·m | 1715.0 ft·lb2325.3 N·m | 1127.1 ft·lb1528.2 N·m |
| A307 | 130.4 kN29313 lbf | 642.6 ft·lb871.2 N·m | 478.5 ft·lb648.8 N·m | 314.5 ft·lb426.4 N·m |
| A325 | 291.0 kN65426 lbf | 1434.2 ft·lb1944.5 N·m | 1068.1 ft·lb1448.1 N·m | 701.9 ft·lb951.7 N·m |
| A490 | 467.3 kN105057 lbf | 2303.0 ft·lb3122.4 N·m | 1715.0 ft·lb2325.3 N·m | 1127.1 ft·lb1528.2 N·m |
| A574 | 539.3 kN121237 lbf | 2657.7 ft·lb3603.3 N·m | 1979.2 ft·lb2683.4 N·m | 1300.7 ft·lb1763.5 N·m |
| Grade | Clamp forcepreload | Dryμ 0.15 | Oiledμ 0.11 | PTFE / moly pasteμ 0.06 |
|---|---|---|---|---|
| Grade 2 | 147.2 kN33102 lbf | 701.6 ft·lb951.2 N·m | 512.7 ft·lb695.2 N·m | 323.9 ft·lb439.1 N·m |
| Grade 5 | 331.3 kN74481 lbf | 1578.6 ft·lb2140.2 N·m | 1153.6 ft·lb1564.1 N·m | 728.7 ft·lb987.9 N·m |
| Grade 8 | 532.0 kN119596 lbf | 2534.8 ft·lb3436.7 N·m | 1852.4 ft·lb2511.5 N·m | 1170.1 ft·lb1586.4 N·m |
| A307 | 148.4 kN33369 lbf | 707.2 ft·lb958.9 N·m | 516.9 ft·lb700.8 N·m | 326.5 ft·lb442.6 N·m |
| A325 | 331.3 kN74481 lbf | 1578.6 ft·lb2140.2 N·m | 1153.6 ft·lb1564.1 N·m | 728.7 ft·lb987.9 N·m |
| A490 | 532.0 kN119596 lbf | 2534.8 ft·lb3436.7 N·m | 1852.4 ft·lb2511.5 N·m | 1170.1 ft·lb1586.4 N·m |
| A574 | 613.9 kN138016 lbf | 2925.2 ft·lb3966.0 N·m | 2137.7 ft·lb2898.3 N·m | 1350.3 ft·lb1830.7 N·m |
Torque for 1-3/8" hex head bolts and nuts, standard ISO/ASME heads on steel with a 36.5 mm clearance hole. Friction μ applies to both the threads and the bearing face. Always follow the manufacturer's value where one exists.
1-3/8" thread and dimensions
- Coarse thread
- 1-3/8"-6 UNC — pitch 6 TPI
- Fine thread
- 1-3/8"-12 UNF — pitch 12 TPI
- Tensile stress area Aₛ
- 745.1 mm² (coarse), 848.2 mm² (fine)
- Pitch diameter d₂
- 32.175 mm
- Tap drill
- 1-7/32 (coarse), 1-19/64 (fine)
- Wrench size (hex head)
- 2-1/16"
- Clearance hole
- 36.5 mm
How the 1-3/8" 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% × 558 MPa × 745.1 mm² = 291.0 kN
T = F × (0.16·P + 0.58·μ·d₂ + μ·Dₖₘ/2)
T = 291.0 kN × (0.16·4.23 + 0.58·0.15·32.18 + 0.15·44.45/2) mm = 1944.5 N·m
Here d₂ is the pitch diameter and Dₖₘ the effective bearing diameter of the head (44.45 mm). Change the grade, lubrication or preload in the calculator below.
Frequently asked questions
What is the torque for a 1-3/8" Grade 5 bolt?
About 1434.2 ft·lb (1944.5 N·m) with dry threads, 1068.1 ft·lb (1448.1 N·m) with oiled threads and 701.9 ft·lb (951.7 N·m) with PTFE or moly paste, for a coarse 1-3/8"-6 UNC thread tightened to 70% of yield. The resulting clamp force is 291.0 kN.
What is the torque for a 1-3/8" Grade 8 bolt?
About 2303.0 ft·lb (3122.4 N·m) with dry threads, 1715.0 ft·lb (2325.3 N·m) with oiled threads and 1127.1 ft·lb (1528.2 N·m) with PTFE or moly paste, for a coarse 1-3/8"-6 UNC thread tightened to 70% of yield. The resulting clamp force is 467.3 kN.
What size wrench fits a 1-3/8" bolt?
A standard 1-3/8" hex head bolt or nut takes a 2-1/16" wrench or socket.
What drill size do I need to tap 1-3/8"?
Use a 1-7/32 drill for 1-3/8"-6 UNC and 1-19/64 for 1-3/8"-12 UNF.