Metric Thread Basics

Metric thread labels show diameter and pitch

A label such as M6 x 1 means a 6 mm nominal major diameter with a 1 mm pitch. A common starting estimate for a cutting tap is major diameter minus pitch, which gives 5.0 mm for M6 x 1.

Coarse and fine metric threads differ

M8 x 1.25 and M8 x 1 are both M8 threads, but they do not use the same tap drill. The pitch is part of the size, and skipping it can lead to the wrong hole.

Use the estimate carefully

The diameter-minus-pitch rule is useful for quick checks, but published charts and tooling guidance are better for final work, especially with forming taps or controlled thread engagement.