Examples of "cheapie retreads" - I got the whole skateboard new from wallyworld for like $12, so I was a touch disappointed but not surprised lol
I spun 'em down on a lathe so they didn't come apart, but they're defo crap - the original bearings in particular are really bad (I'd never give such a board to any kid), but as they're just idlers/redirects for a recumbent I replaced the bearings w/quality ones I happened to have & used them anyway...
The inner core is a
hard plastic compound w/air pockets which amplifies the vibration from chain clatter, the outer just some cheesy soft plastic & really easy to peel... I suspect they'd not last twenty minutes scrapin' asphalt.
Nevertheless, for super inexpensive idlers they work well enough so any decent set of skate wheels too worn for a board would be awesome indeed - I bet any local bike/board shop would have a pile of them they'd love to be rid of. As ya can see in the pic, just pull the bearings and use a nut, bolt & washers to chuck it up in a lathe/drill press or even a hand drill with the cutter in a vice or whatever (carefully ofc lol), it's really easy.