Bolt Torque API

Bolted-joint torque, preload and stress maths as an API, computed locally and deterministically for ISO metric fasteners. The torque endpoint applies the torque-tension relation T = K·D·F — the tightening torque equals the nut factor times the nominal diameter times the bolt preload — and solves either way: the torque needed for a target preload, or the preload achieved by a given torque, with the nut factor K capturing the lubrication condition (≈0.20 plain, 0.16 plated, 0.12 lubricated). The stressarea endpoint computes the tensile stress area from the thread geometry, As = π/4·(d − 0.9382·P)² — the effective cross-section that carries the load — together with the nominal shank area and, given a proof or yield stress, the proof and yield loads of the bolt. The preload endpoint sets the clamp force as a percentage of the proof load (75 % is the usual target for reusable joints), F = (percent/100)·σproof·As, and returns the resulting tensile stress and, with a diameter and nut factor, the tightening torque. Grade proof stresses for 8.8, 10.9 and 12.9 bolts are documented. Everything is computed locally and deterministically, so it is instant and private. Ideal for mechanical-design, assembly and maintenance tools, torque-spec generation, fastener selection and structural-bolting apps, and engineering education. Pure local computation — no key, no third-party service, instant. Live, nothing stored. 3 endpoints. This is bolt tightening and preload mechanics; for thread pitch/lead geometry use a thread API and for bolt-circle hole patterns use a bolt-circle API.