Keep in mind that punches get worn out and some don’t mark as deep as some of the others and punching numbers/letters is a tedious job. Hard to get straight and when you are on an assembly line you only have so much time before the next one is there to be stamped.
Yea i was wondering that , I retired from Trenton Engine Plant From 95 till 2017 and they just started using they pin stamp then and i talked to people that were there in the 60s and that is what they said
