No number on mine that I can see. The hole in the end is just over 5/32. The one in the side is a bit larger but also not very round so may be damaged as the tool has been used hard.
Come to look at it, yours really is rode hard! None of mine show this much wear.
Making a rivet head look real pretty with a hammer alone, is harder than just using the dome part on one of these.
The dome makes it all smooth and rounded with just a couple swats at the end, and folds down the "hem" the edge of the mushroom, real nice.
Maybe some people can just use the rivet set for the whole shebang, but I am not this good. I will bend the rivet if I try to use just the set alone. So I peen until the mushroom is formed well all around, and then, the set.
I have made a couple of my own sets out of hard bolts. Just the dome part, for finish work.
Just cause I can't find enough rivet sets. Bolts don't work as good, they have so much less mass.
But its better than poke with a sharp........
I don't get to use copper washer/rivets (rivets n roves as they said) very often anymore.
They jacked up the price some years back.
I still have some but now they are kind of precious.
yours Scott