I had a set of five 15x6 16-spoke 5000 turbo alloys machined to fit my
Syncro.  What I did was to drop off a stock Vanagon alloy along with the Audi
rims and have the shop machine the center holes to match.  Now they take the
stock Vanagon Carat center cap, which fits snugly, is easy to replace should
I lose or damage one, and looks pretty damn snazzy, to boot, IMHO.  I could
measure the exact dimensions with verniers if anybody really wants to know.
The stock lug nuts for steel wheels have the proper 14mm ball seat for these
rims.  Inexpensive plastic lug nut covers jazz 'em up.
-christopher