I've reamed many arms over the past 30 years. This was the first time I found an arm that was unreamable. my reamer wouldn't touch it. But the file worked great. I should have sent you my arms and my reamer and have you go at it. I spent an hour on one arm and got nowhere. It was like trying to saw a car tire in half with a stick. I even took the reamer bit out and stuck it in my drill. Then I froze the arm to make it harder in hopes of being able to get it to cut. Its a brand new Hudy reamer. The chainsaw file worked in a matter of seconds. Just trying to give people a heads up so when they build the kit they know how to get it right. And the problem is, the pin wont slide through. When the mold cools the two ends of the arm angle in toward the center and makes the holes offset, so its not a straight shot through the arm.