The last set fo Mark Willaims steel caps I put on one of my 8 3/4 rear ends had a specific inside diameter, +.0010. I took the third member and the new cap to a local machine shop and they let me fit them on my own using thier Sunnen rod machine to surface the new caps to get that dimension set up corectly. I took my own inside and outside mikes along to do the measuring I ended up being within .0002 from the max I.D. at room temps