Thread Size Comparison Table

Thread Size Comparison Table

This page converts thread sizes from inches to millimeters (metric) and from millimeters back to inches — a conversion used often in screw, nut, and industrial work, especially when comparing UNC / UNF / BSW threads with metric (M) threads.

There are two main thread systems used for screws and nuts: the imperial (inch) system and the metric (millimeter) system. The two cannot be used interchangeably, but their sizes can be matched to the closest equivalent for general use. This comparison is known as the Closest Metric Equivalent — the metric size nearest to a given inch thread.