Milspec Trigger

Had problems with a milspec trigger pin walking left and dropping inside, stopping the trigger from working. Picked up a set of the cheaper anti walk pins with a Torx screw on each end. Works like a charm. Found the guy who put my Spikes lower together used the hammer pin on the trigger. Duh!

My question on the milspec pins... one pin has a center notch and end notch. The other just the center notch. I know the end notch is for the hammer spring tip, to do the whole anti walk process and hold the trigger pin in place. And the hammer pin doesn't need one, because no spring tip to lay on it.

Anyway, why are the trigger AND hammer pin notched in the center?