Chrome center hubcaps.......

My center hub caps inside diameter measure 7 5/8 inches. A seller of those center caps told me that his measure 8 inches exactly? I have '97 chrome wheels on my '90 hubs. Those wheels fit the hubs perfectly. Since the bolt pattern is the same with the '90 and '97, why would the seller tell me that his center caps won't fit? The caps are held in position by the lug nuts. If the lug nuts are in the exact same position, why would his center caps be 3/8 inch wider than the '90 center caps?

I'll answer my own question here since I elected to by the '97 lugnuts by mail order. With the '97 lugnuts, the caps will install properly. However, the lugs on the '90 are 1/2 inch and the '97 lugs are 5/8 inch. The holes in the '97 wheels are 1/16 inch too large for the '90, and the 1/2 inch lugnuts seat in too deeply but work for now. I have the caps temporarily installed by putting rings of cut tubing onto the 1/2 inch lugnuts that give the same circumference as the rings on the '97 lugs that the center caps attach to. Next job is to buy the 5/8 inch lugs and grind the attachment area of the studs to fit the '90 axle flange and brake rotor hub to have a proper attachment for the center caps and a proper repair. That will have to be done by using a metal lathe and grinder, or by using a drill press to hold the stud while it's being ground to size. It has to be ground instead of machined because the stud is hardened for strength after production. A carbide cutter would go dull or break if used on the stud now.