Tightening Torque Spec Table

Bolt tightening torque depends on thread and bearing-face friction coefficients, strength grade, and lubrication. This reference provides recommended torque values per ISO 898-1 and VDI 2230 for grades 8.8, 10.9, and 12.9 across M3–M48, tabulated for both dry (K=0.20) and lubricated (K=0.15) conditions. Preload (Fp) is set at 70% of the yield stress. Over-tightening leads to bolt fracture and reduced fatigue life; under-tightening causes joint loosening and slip — use a torque wrench for controlled tightening, and consider the turn-of-nut method when friction is uncertain.