7/16-20 UNF Torque Spec
Calculated preload torque by grade, plus what actually changes the number.
By grade
| Grade | Dry (lb-ft) | Lubed (lb-ft) | Dry (N·m) | Clamp load | Ultimate tensile |
|---|---|---|---|---|---|
| Grade 2 Low/medium carbon steel, unmarked head | 35.7 | 26.8 | 48.4 | 4,897 lb | 8,784 lb |
| Grade 5 Medium carbon Q&T, 3 radial head marks | 55.2 | 41.4 | 74.8 | 7,568 lb | 14,245 lb |
| Grade 8 Medium carbon alloy Q&T, 6 radial head marks | 77.9 | 58.4 | 106 | 10,684 lb | 17,807 lb |
| 18-8 SS 304/18-8 stainless | 26 | 19.5 | 35.2 | 3,561 lb | 8,903 lb |
Why lubrication changes everything
Roughly 90% of the torque you apply is consumed by friction — under the head and in the threads. Only about 10% becomes useful bolt stretch. That means the friction coefficient, not the bolt, sets the relationship between torque and clamp load. Here is the same 7/16-20 UNF Grade 5 fastener under different conditions:
| Thread condition | Nut factor K | Torque for same preload |
|---|---|---|
| Plain / as-received, dry | 0.20 | 55.2 lb-ft |
| Zinc plated, dry | 0.22 | 60.7 lb-ft |
| Black oxide, lightly oiled | 0.18 | 49.7 lb-ft |
| Machine oil on threads | 0.15 | 41.4 lb-ft |
| Molybdenum disulfide / anti-seize | 0.12 | 33.1 lb-ft |
| Waxed or PTFE coated | 0.10 | 27.6 lb-ft |
Assumptions behind these numbers
T = K × D × F with K = 0.20, F = 0.75 × proof load, and proof load = tensile stress area (0.11872 in²) × the grade's proof strength. This is a general-engineering starting point for a reusable steel-on-steel joint. It is not a substitute for a manufacturer's torque sequence on an engine, a suspension component, a pressure vessel or any structural connection.