SLUGGER R0550 Purge Plug. More details: Purge Plug, Roto 1, The Roto-Star Optional Purge Plug Is Ideal For Welding Stainless Steel Or Aluminum Or Alloys, The Purge Plug Enables You To Easily Fill The Unit With Inert Gas To The Optimum Level, Which Maintains The Quality Of The Welded Stock And Prevents Color Alterations, For Welding