Can I get replacement caps and also what size should they be I see different sizes 56 57 58?

 

Which Jag wheels do you have on now?

 

I purchased Black replacements for my X-Type from Welch Enterprise. The 56, 57 and 58 refer to MM's. Measure the center opening and determine if it is 56mm or 57mm or 58mm. Then order the appropriate size and the desired color.
The old ones can be pried out with a screwdriver and the new ones popped in.