Grace g-940 arm mount????

Hi, I am in the process of putting together a SP 10.
I am mounting a Grace g-940 and the instructions call for a 15/16 - 1" hole for the base shaft however the base shaft is 5/8" in diameter and I am wondering why you would want all the play when the overhang is to be no more than 1/8"+or-. My thought is that the hole should be just slightly bigger than the base shaft. What am I missing??
Also I am using rock maple for the arm board, if I made a brass bushing to take up the slack in the hole that is already drilled would this work?
Also I am looking for suggestions for footers and a platter mat.
Thanks
Richard