ef ghia rims, centre cap size different. wtf?

[EL_futuraistic]

Hey guys. I have a set of ef ghia rims, 1 was slightly damaged and so i picked up another 2nd hand one. However my centre caps do not fit this rim, aparently there were two sized centre caps??? Does anyone know of this, and where i can get another centre cap? I have tried ford and i would have to order one except they are $20.

Just wondered if there is anywhere that i could get one cheaper?