Actually, these fit the whole M&P line as well as the S&W 1911 sights. It's a 3/16 pin with a half round head. It's flat on the bottom and the flat edge fits on the first step of the sight. It just works better than the round pin. Not essential, but very handy. It can also be used to some advantage on a Novak style sight, assuming the dovetail is 3/8" or wider.