Diameter tolerance or out of round? It's probably not too big of a
deal for most applications especially if you're going to split/slit and
clamp it.

You're probably better off erring on the side of slight interference if
you're splitting and clamping and adjustability is not very important.

If you're looking to make a sliding adjustable joint, I'd keep a nice
tight tolerance, maybe no more than a few thousandths of an inch if you
can do so. If you can't, it's not a big deal, but a good mechanical
fit will allow sliding while still giving lots of strength.

If you make the fit loose (10 thousandths) you're going to be relying
on your hose clamps or bolts to do all the holding and you're probably
going to really only get contact under the clamping points, which is OK
in a lot of applications. A better fit will spread out the clamping
force more.

73,
Dan
N3OX