Steelie Center Caps

I've got K11 hubcaps (7 inch silver center caps from silver steel wheels) and I want to put them on the 15 inch black steelies on my K12 Micra.
From the look of them, they push onto the wheel bolts and 'click' into place. Only problem is when I push them on the wheel bolts they aren't secure.
How do I get them to stay in place? Do I need K11 wheel bolts? Or glue!?
Already asked on the K12 board but realised the place to ask is the board where people actually have them ;)

Sith
 
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