Screw Size Chart

How to use this chart

This chart pairs each metric screw size with the imperial size closest to it in diameter, so you can find a rough substitute when a project or parts bin mixes the two systems.

"Closest imperial equivalent" means diameter proximity only — it identifies the inch size whose nominal diameter is nearest to the metric size in the same row, not a size that is guaranteed to fit the same hole, nut, or tapped hole.

A close diameter match does not by itself make two fasteners interchangeable. Metric and imperial (UNC/UNF) threads use different pitch conventions — metric pitch is measured in millimeters per thread, imperial in threads per inch (TPI) — and different thread forms, so a bolt and nut, or a bolt and a tapped hole, must match on pitch and form, not diameter alone, to thread together correctly.

Before treating two sizes on this chart as interchangeable, check the actual mating hardware: measure or match the thread pitch/TPI with the thread identifier, or convert precisely with the metric to imperial screw converter. See thread types for how diameter, pitch, and form together define a thread.