Model 10 / M & P Center Pin question

[postoak]

I've got two center pins in front of me for 4 inch revolvers. One has the stop collar 0.800" from the cylinder end and the other is only 0.700". The two revolvers I have take only the 0.800". What's the 0.700" fit?

 

[tennexplorer]

An earlier version. If I remember right (could be totally wrong) the .700" is pre-war.