In the English system, the pitch is expressed by the number of teeth per inch, and the metric pitch corresponding to 25 teeth per inch is:

1 inch /25 = 25.4 mm /25 = 1.0 16 mm ≈ 1 mm.

Pitch (metric): the axial distance between the corresponding points of two adjacent teeth on a thread.

Pitch (English): expressed by the number of teeth per inch of thread.

The pitch comparison table of English and metric threads is as follows: