Not sure what you mean radius or diameter, see the shiny part on the very tip of the hub in the pic? That's where we lathed it down about an 1/8 inch, just enough so that the hub could fit thru the center cap area if needed. I'm about to do this again, going further in because my new wheels need to sit further in to run a 315 tire. My current setup doesn't quite stick out so far that it goes thru the cap area, I have 18x10 wheels with a +42 offset, running a 7/16 spacer. My front fenders have been pushed out about 3/4 inch. I may have to run without a dust cap on the new wheels to run a center cap. American muscle no longer sells the exact caps in the pic, you may be able to find something similar.