20 threads per inch is a numerical measurement, of thread pitch frequency and is the standard
that manufacturers of pedals and crank arms try to match, some minor QC variations exist.


Course is Not a Measurement , but a category, in machines some places there is a course and fine thread ,

like Swedish cars in the 60's using some German Parts , the wrench hex may be the same but the Bolts are different.

The 1/2" pedals also used a 20 Tpi standard pitch

France tried to be unique for a while ..14mmx1.25 TPmm, but fell back with the rest , for having an export market.



'/,