Not exactly sure sure which pin you are referring to,can you be a little more specific ?
the pin that secures the locking bolt?
.050", same as front sight pin when present.
That's one part I have never needed t remove from any S&W I have ever owned over the past 30+ years. A small shot of Gunscrubber or brake & Parts cleaner has always taken care of any dirt in there for me. I especially try and keep from removing any pins unless necessary for replacing parts. Too easy to bugger up the gun and reduce it's value. If you have to , be sure to use CUP HEAD punches.