Snap On MW120 MIG Welder

If it has a tweco mig gun then go to tweco for the liner. A snap on dealer can get you the parts but expect big $ for a small cost.
If you bring the gun assembly to a welding supply dealer they should be able to match up the liner.
Being it is a 120- what is the plug on the wall side? 120vac or 220vac?
That and the wire diameter will dictate the steel able to be welded. Also duty cycle will dictate how long you can weld for.

SN: I own my own welding shop for 27 years now but a welder for almost 40.
PM me if you have any questions.
Syleng1