I was installing a new differential cover, and I think I stripped one of the bolt holes on the differential housing. I did some research and need to insert a 5/16"-18 Helicoil, which requires drilling the hole using a 21/64" drill bit. My concern is that I only have a hand-held drill, not a drill press. What can I use or fabricate to ensure my hand-held drill stays centered while I drill the hole? Any ideas?