UNI ISO 4755 (identical to ISO 4755) specifies the dimensions of thread run-outs and thread undercuts for ISO metric threads (according to ISO 261 – general purpose metric threads).
: It provides clearance for the assembly of mating parts (like a nut or a flange) to sit flush against the fastener's shoulder, as threads cannot be cut perfectly to the very edge of a solid wall. : The undercut dimensions are determined by the thread pitch ( Diameter ( : Typically at least smaller than the thread's minor diameter. : Generally recommended to be between for normal applications. Transition : It often includes a radius or chamfer (e.g., 45 raised to the composed with power tabella gola uni iso 4755
(Undercut Width): The axial length of the groove. A common rule of thumb is that the undercut should be roughly times the thread pitch ( Informative Report: UNI ISO 4755 – Thread Run-Outs
Connecting rod bolts and cylinder head bolts almost always conform to an undercut standard (often derived from ISO 4755). When rebuilding an engine, mechanics look for this groove to confirm they are using OEM-grade fasteners, not cheap hardware store substitutes. Passo (P) – Thread pitch (mm) g (min)