New Trigger for S&W M&P 15

[popeyespappy]

I want to put a new trigger in my M&P 15. I think I'm going to go with the Rock River Arms 2 stage national match. I "Think" I need the small pin model but as I have no idea what the difference between small pin and large pin is I don't really know.

Can someone shed a little light on this for me?

 

[Dfariswheel]

Generally, the large pin is used mostly on Colt rifles, but also on several others.

The large pin hammer and trigger pins are .176 in diameter.

The small pins are .156.

The S&W (as I recall) is supplied to S&W by Star in the form of unfinished parts.
It takes the small pin trigger unit.