The nut for the liner sticks out too far, preventing the gun to welder connection from fully engaging. That prevents the thumbscrew from going in as well as the gas port will not fully line up. Nut look to be the right part .
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Reply:I am wondering if that liner is for a gun that came with a later model Handler like the 135, 140, 175, 180, 187, 190, and 210? The Handler 120 came with a different gun then the above units.
Reply:Were you installing a new liner? They often have to be trimmed a bit (they leave them long on purpose). If the liner is too long you won't be able to tighten the nut all the way.Check out my bench vise website: http://mivise.comMiller Syncrowave 250DXMillermatic 350P with XR AlumaProMiller Regency 200 with 22A feeder and Spoolmatic 3Hobart Champion EliteEverlast PowerTig 210EXT