I have not been able to find data on metric sized barrel plugs for pistols.
Pitch in the USA is measured as how many turns are required to move a nut 1 inch. Metric pitch is measured as how many millimeters a nut moves for 1 turn.
I compared the thread sizes used by Greenmountain and Rayl with the available metric taps and dies. The result was these two tabels. Thought they might be of help to someone.
Best regards
Rolf
