What is the pitch of thread M 16.5? It seems to be English.

The pitch of thread M 16.5 is 1 1 tooth (coarse tooth) or 18 tooth (fine tooth).

Look it up in the table. Generally, English threads are not marked with millimeters. In the English system, the pitch is expressed by the number of teeth per inch. The pitch is 1 1 tooth, that is, there are 1 1 tooth per inch, which is equivalent to 25.4/1= 2.309 mm in metric system.