I don't have a micrometer either and had to look up what a vernier was despite being pretty sure I didn't have one. Are you going to try and make strap buttons out of brass?
That is what I was thinking, we also have some ‘standard’ 1018 steel, although the brass should hold up well if one is not using a ‘straplock’ type system where it has contact with something hard.
Maybe make some prototypes out of aluminum for checking fit.
The key here is ‘downtime in the machine shop’, currently one of the machinists is out because he is in the high risk category. So we are pretty busy right now, but “government jobs” usually get snuck in here and there.
Rob thanks for the pics, that will give me a good ballpark. My current strap locks are about 3mm smaller on the head part.