As Downsy has mentioned, the Dekagrams come with an alloy center cap which is held on by three Allen head screws (but there are two short 'fake' ones threaded into the cap to make a symmetric 5 screws showing) which thread directly into the center section of the wheel itself.
I decided to replace mine with some 316 marine grade stainless Allen screws from McMaster-Carr because; salt soup.
dhminer just elected to leave them off (which yes, looks more 'race car'), and I would possibly do the same except that the treaded holes for the caps then show, once close to the car.
There is a Konig, silver on black center, also aluminum alloy badge 'medallion' which goes into the recess of said center cap, and I have been trying myself to find some ST gel badges of the same size to replace the Konig stickers (I would prefer some M-Sport ones, but they would have to be custom made and just not worth the coin required to do that).