I doubt they would fit right on alloy rims, as alloy rims don't have the same kind of lip, the hub caps clip on to the oposide side of the metal then the tires bead and the lip on a steel rim is rolled steel, creating a lip with an edge, an alloy rim has a smooth cast lip without much for the clips to bite in to, I've seen the aluminum moon disks screwed on to wheels, and they looked fine, they sell moon disks that are designed to screw on, otherwise I would epoxy on some T-nuts, and use small alloy bolts.
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