The Purge Plug Back Purge attachment allows for welding ends on features, such as ferrules and field applications, where traditional flow through is not available. It utilizes any size purge plug with a spring loaded end cap that is machined to fit the I.D. of your work piece allowing you to purge in reverse. This piece pays for itself in gas savings alone! Where in the past you would have to purge a whole line for one weld, Purge Plugs can get it done with only purging the final 6″ before the weld.