Since most people don't have the pivot pin installation tool, go to a hardware store and buy a clevis pin. A clevis pin has the hole drilled in the end and makes it quite easy to install the front pin. I believe it is 1/4" dia.
I have built many lowers and it works great.

If you plan on using a .22 conversion, 22 dedicated upper or 9mm upper w/ ramped bolt, you will need to swap the RRA hammer to a smooth face hammer such as DPMS.
(The RRA has a nothced hammer)