Torque only turns into bolt load through the nut factor K. Get K wrong and the bolt load is wrong by the same proportion. This guide summarizes PCC-1-2026 Appendix K. A printable PDF (PB-TD-214) is below. Values are for reference; confirm against the current edition of the governing standard. Send us your bolting list for a quote or call (281) 581-0176.
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The short formula
T = K × D × F / 12, where T is torque in ft-lb, D the nominal bolt diameter in inches and F the bolt load in lbf (App K-1). K is roughly the thread and nut-face friction coefficient plus about 0.04.
Typical values
| Bolting | Typical K at room temperature | Note |
|---|---|---|
| SA-193 B7 / low-alloy, lubricated | 0.16–0.23 | App K-1 |
| SA-193 B8M stainless | About 30% higher than B7 | With the same lubricant |
| Torque index tables in App O | Given at K = 0.15, 0.18 and 0.20 | Root-area basis |
How much it matters
- Going from K = 0.10 to 0.30 triples the torque for the same load.
- One lubricant tested between 32 and 100°F changed K by about 50% (0.155 to 0.105).
- A lubricant’s maximum temperature rating does not tell you how it will perform at disassembly or what K it gives.
- Use test results for your own lubricant, bolting and coating where you can.
Detailed formula
App K-2 gives a fuller formula that splits thread pitch, thread friction and nut-face friction (the VDI 2230 approach). In that appendix the default bolt load is a percentage of yield on the tensile stress area, while App O uses root area. Make sure your torque table and bolt load use the same area.