The OEM hole is drilled in a raised boss on the wheel. I suppose there is a
question if it is to provide flat surface for the OEM center cap to rest/register
on, or whether it is meant to add the material removed in making the
drilled/tapped hole.
I would be tempted to drill and tap two more holes in the wheel at the same
radius as the OEM hole in a triangular pattern. (Slightly longer nylon spacers
would be needed for these holes/screws.)
Just for the record, given the usual "righty-tighty, lefty-loosey" screw threads,
is there a tendency for screws to unscrew themselves on the wheels on one
side of the car? If so, which side?
Also, thinking of possible electrolysis due dissimilar metals goobering up the
threads on the screws, given the need for a secure, reliable attachment, what
type of screws would be
best; mild steel, stainless steel, aluminum,
nylon?