Technical wheel help

i am trying to find baby moon caps for my truck. I measured the inner circle of the rim. it measured 7.5 in. i order a set from coker and they are too big. am i measuring it wrong or what?

 

The wheels look like solids,do you know who makes them? HRP

 

no clue they were on the truck when i got it

 

any help would be awesome

 

Look like std 6 lug chevy.Get a measurement just in front and behind the 3 tits(diameter).

 

Look like they may be an after-market wheel that may use the GM car type Rally center caps. See if you can try one and if it fits there are various caps with that type of mount. Also the dust cap on the truck hub may interfere with some of the Rally style caps.