Center "cap" for aftermarket steering wheel - doesn't fit

I thought this 9 hole center "cap" might fit the recently acquired aftermarket steering wheel, also with a 9 bolt mounting setup.  It doesn't fit.  The bolt diameter for the center cap is slightly smaller than that of the steering wheel, by maybe 3 mm.  The center cap is machined out of a block of aluminum billet and looks to be a one-off handmade item.  I have other 9 hole patter steering wheels.  I'll have to check to see if the bolt patter fits one of them...