I've been searching everywhere for a center cap for my Enkei Racing RPF1 wheels that would hold the Factory Five badge and I finally found the perfect center caps at Ace Hardware for only $2! This is a 2.5-inch "Knock Out Seal" by Hillman, #58179-F. All Ace Hardware stores do not have the Hillman fastener line, and all may not stock these nylon caps for plugging desk holes. I got them in black but others are in grey so you may have to paint them, but they snap in firmly and have a flat face for the FFR badge.

The Enkei center caps fit the wheels, of course, but are tapered so the Factory Five badge doesn't fit. My cost for discovering this? $104.