Here is how I got the chrome beetle hubcaps to fit my steels.
This is the back of the chrome cap, it needs to be cut where the white line is, but leave a bit extra to allow adjustment
Get an M6 x 40mm bolt and assemble a penny washer ( holes drilled around the edge to help bonding it in) and nut, and use a dab of superglue to lightly hold it in the centre of the cap, you can't see it here, but there are two clips in the centre which the bolt head just sits between, making finding the centre easy.
I used a 2-pack structural adhesive to fill the central recess and so bond the bolt and washer into the hubcap.
Drill a 6mm hole in the centre of the black centre cap, there is a mark on the back, dead centre.
Assemble the two caps together with a nut and washer either side of the black cap, so that it doesn't distort when tightened up. Now, the time-consuming bit, the previously cut-down legs on the chrome cap need to be adjusted a bit at a time to get the cap fitting into the wheel nice and firmly, I found when I got it right, I couldn't pull the cap off with my fingers. Now I am happy with the fit, I will bond the two caps together to make it even more solid.