UNC Tightening Torques
Tightening Torques for UNC Austenitic Stainless Steels (A2 & A4)
| Thread Diameter | Friction Coefficient | Tightening Torque (Nm) Property Class | |||
| 50 | 70 | 80 | Bumax 88 | ||
| 1/4-20 UNC | 1.6 | 3.6 | 7.7 | 10 | 11 |
| 5/16 - 18 UNC | 1.6 | 7.3 | 16 | 21 | 22 |
| 3/8 - 16 UNC | 1.6 | 13 | 28 | 37 | 39 |
| 1/2 - 13 UNC | 1.6 | 31 | 66 | 89 | 95 |
| 5/8 - 11 UNC | 1.6 | 61 | 131 | 175 | 188 |
| 3/4 - 10 UNC | 1.6 | 108 | 231 | 308 | 329 |
| 7/8 - 9 UNC | 1.6 | 172 | 369 | 493 | 527 |
| 1 - 8 UNC | 1.6 | 258 | 553 | 737 | 789 |
The Torque recommendations are calculated assuming a friction coefficient of 1.6 which requires burr-free surfaces lubricated with a good quality lubricant. Stainless Steel Fasteners tend to seize while being assembled (tightened) The risk of seizing is reduced by:
- Using Fasteners with smooth clean threads (Rolled Threads)
- Using Molybdenum Disulphide Grease)
- Tightening the screws with low rpm's without interruptions)
The tightening torques stated result in a 90% utilization of the yield strength. Conversion factor: Nm to foot pound = 0.7376 Nm to inch pound = 8,851
