Usually an aftermarket wagon wheel will have it's own style of center cap that just passes through the wheel with a slight lip on the back to hold it in place. And the ones that are flat in the middle won't have room for a screw to pass out the back side without causing issues with the wheel sitting flat on face of brake rotor/drum. If I'm reading everything correctly and remembering my wheels. Seems like a Ford wagon wheel is embossed around the lugs for the center caps to screw to?
Randy
Mt. Airy, NC 81 F-150 STYLESIDE regular cab 2wd. 302 Auto Zone crate. 5 spd M5od-R2