Please provide measurement for stock center cap

Will someone who has these on their Jeep, please provide a measurement of the width of these things:
http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&category=43961&item=7960455659&rd=1

I want to see if they will fit into my new 15x8 Cragar Soft 8's, I get 3 1/4 opening on these. I am hoping they would look good together (matching black color and gloss), but I am not sure because I have not seen them together yet. Though it might be a good look!?

Thanks

uhm they have to be screwed on from the back .did you now this? so you would have to drill holes in your rims to make them work and that is is they even fit right on the rim .

Okay then, scratch that idea. Thanks for the quick reply. I might just spray paint the rust black or fab some black center caps on my own, I hate chrome.