I just observed while putting my junk sliders to bed in the junk box.
I recon that they might be sleeved internaly [which i'd never considered] but never quite studied them like this.
Am i just slow & everyone knows, or does it just look that way.
photos.app.goo.gl/p6sCnpv8KoP5HezU9

I don't know the answer but they do look that way. If the sleeve has iron in it a magnet may tell.

Hi, SMGLSMKR it'll be alloy for sure but i'll machine up where i must've cut it off long ago--no idea why i did that lol--& i'll machine to see if it 'just looks that way' or is in fact a sleeve.
It'll be original & doubt anyone would go to 'that extreme'.
My shed is a mess--lathe in there somewhere haha. Cheers.

Ok, i'm dreaming. Machined up the end of the cutoff slider i had & no sleeve.
So still not convinced i cut it longways. No sleeve insert.
So i give up.
Mind you, the one i cut didn't have a step at the top like in my pic.
Not gonna cut that one as is usable at a pinch if i'm stuck.

Never saw a sleeved outer tube.  Closest is the ones with replaceable  top and bottom bushes.

My observations as well.