J.B. Weld is very good for filling, but I was told it would not work under powder coating; hence my inquiries which led me to Lab Metal. I have a tin, but haven't had reason to use it yet.
I polished a few No32 tubes on a wood lathe by mounting between a dead center in the spindle and a live center in the tail stock. The cone of the dead center fit the objective end of the stripped tube and the cone of the body on the live center happened to be about the right size to fit into the ocular lens retaining ring. One had to be careful not to put too much pressure on the tube or the files/paper!