Metric threads are common in DIN, ISO and many global engineering systems. UNC and UNF threads are common in inch-based applications.

UNC has a coarser pitch, while UNF has a finer pitch. Thread mismatch can damage parts, delay assembly and create safety issues.

Always confirm diameter, pitch, tolerance class and thread length on drawings or purchase orders, especially for replacement hex bolts, hex nuts and flange bolts.