11/16in to 2in spool adapter (for small welders that can still fit a 10 or 11lb spool.) You should be able to just print the upper and lower *(maybe a spacer or two.)

Others either didn't hold it tight enough for the right friction, or they let it hit a screw that my lincoln has in the panel behind the spool. This will keep it away from that screw and still use the original nylon thumb-screw, all while keeping the spool from unwinding* (also I remodeled a printable thumb-screw.)

No supports should be needed on main upper and lower. I used .2 layer, .48 width, 2 walls and pretty sparse infill, and it seems pretty solid.

Printable thumb-screw is just a bonus, the original should work. If you do print it, use 0.4 to 0.5mm line width at most, leave in this orientation, and enable supports. Having a 3/8 nut on hand to work the threads in or test fit is recommended.

(*) Spacers are also optional, but allow for fine tuning the tension/friction. I might have made it a little loose, so I could use spacers to keep it from jamming or aggressively unwinding itself... might as well print a couple, just in case. I couldn't decide whether spacers should go on the adapter with the spool or on the post before the adapter, so I uploaded both.

1.3 update: screw was too long and the handle sucked. should be better now. Also reuploaded all files in higher res.