I've got an odd tube I'm considering turning into an F1 can. It's an old CZ .22 upper. The tube is about 6" long, and the barrel ends inside, about 2.75" from the end of the tube. Basically it would be an integral.
edit - (CZ v22(?) upper with a big aluminum tube for a handguard)
One end is threaded for a barrel nut. (CZ .22 upper)
The other end is plain OD 1.92" / 49mm, ID 1.63" / 41.6mm, wall 0.14" / 3.7mm

My initial thought is to thread it for a standard or somewhat common endcap, if there are any standard threadings compatible with those tube dimensions.

My second thought is to have that tube ID threaded to match an OD threading on another tube. (extender, retainer for first baffles) The other end of the second tube having a common / easily available endcap threading.

Any thoughts?

I wouldn't plan to use your existing tube. It's only going to drive a design you don't want and is unnecessarily large, thick, and heavy.
A 1x6 is all you really need, but you can make it a bit fatter if you're going for a certain look.
You can even put a 1x6 design inside a larger (fake) tube, to give the look, but only using 1" internals (less costly).

The existing tube is already on the rifle - it's the existing handguard. It's going to be there anyway, so why not use it?

Ahh! It would've been helpful if you put that info in the OP. It was my assumption you bought or had a tube (you didn't say handguard) made and never built it out.

Are we talking a V22 or something like them?
The gross volume isn't going to be the best suppressor and not allow for a selection of "parts". (are you making your own baffles?)
All you'd end up doing is threading another tube (silencer) to the front of this one (as you said)
You're best and easiest solution is a 1x6ish design (something like the XRT)

yeah - I think it's a vz22. I'm pretty sure those don't take regular AR22 mags. I'll have to look into that. I'd hate to build an oddball one-off integral on an upper I can't get replacement mags for.
(edited post to include that)

I'm not entirely sure how I'll come up with baffles. Getting a small/midling lathe is in the plans, but it's not an RFN thing. First I should probably find someone local to give me a Spinning 101 lesson or two.

Yeah, I'll stick w/ the XRT recommendation.
Look at these parts. You can get it so all you need is a drill and a file.