Originally Posted by MattDub

Hello Cain,
To obtain the highest durability we chose 100% nylon on the arms and unfortunately the shrink rate with this material is somewhat high. We worked with manufacturing to try to eliminate the need for reaming and could not come up with a solution.

Glass filled arms (that many other manufacturers use) require less reaming but are not as durable. Hopefully, the increased durability outweighs the need to ream the arms.

I personally use the chainsaw file with a drill, others like the hudy reamer or the #19 drill bit. It's mostly personal preference. 5/32 chainsaw file is 3.97mm and slightly smaller than the 4.0mm hinge pin. Recommend moving the arm around a little while using the file with a drill. This will help enlarge the hinge pin hole slightly. Goal is to enlarge the hole just enough for the hinge pin to fall through by gravity (and maybe a slight tap) alone. Reaming it too far will cause excessive slop in the suspension.