When asked how to put hubcaps onto a rim, I'd reply

With the palm of your hand, right on the edge...

Or am I missing somthing?
Are we talking 'bout some weird hubcaps that install strangely?

Mine, and all the VW hubcaps (metal or plastic) that I've ever seen just 
pop on with a good thump.

Cheers,

SStones,  Toronto Ont. 
<sstones@io.org>