How to Read a Thread Designation (M10 × 1.5 6H)

A thread designation lists the thread type, size, pitch and tolerance class. Reading it correctly is how you choose the right gauge.

Metric: M10 × 1.5 6H

M means a metric thread. 10 is the nominal diameter in millimetres. 1.5 is the pitch in millimetres. 6H is the tolerance class, with H for an internal thread. An external thread would carry a lowercase letter, such as 6g.

Unified: 1/4-20 UNC-2A

1/4 is the nominal diameter in inches. 20 is the number of threads per inch. UNC means Unified National Coarse, and UNF is the fine series. 2A is the class, where A means an external thread and B means an internal thread.

What to send us

For a quote, send the full designation, or a drawing, on our quote page. See also how to choose a thread gauge.