Three Minute Metrology Guide

The issue An O-ring is only as good as the gland it sits in, and every sealing-failure investigation eventually arrives at the same unglamorous place: the groove. Its diameter — always larger than the bore that hides it — carries some of the tightest tolerances on the drawing, routinely ±0.

The issue An internal thread has three diameters, and the one that governs fit — the pitch diameter — is the one no ordinary instrument touches. It lives between the crests, on the flanks that actually locate the mating part, routinely toleranced tighter than either diameter you can see. When a thread

Formula 1 runs on a rulebook, and in 2026 that rulebook was rewritten more completely than at any point in the sport's history. Buried in the new power unit regulations are exactly two clauses held to a tolerance of ±0.1mm — about the width of a human hair,