I like that idea Rez. What is that piece? about 1/32 thick?
Thats how I judge. I eyeball 1/32 of pin stilling out thru washer. And a small file will work great to knock it down some and continue to peen. Just be careful of the scales. I've even been told that a soda can cut up to get a thin piece of metal with a small hole in it to protect the scales while filing the pin head.
Just for the record, I found my calipers and my other gauge. One I use for collarless pinning and it is 0.050” and the one for collars, as pictured 0.034”
The 0.034 is kind of thin for collarless pinning.