I tried making a leak down tester out of 1 of the plugs I changed out of it, after I cleaned out the porcelin, I epoxied ( quick steel putty epoxy ) a 1/4" coiled air hose 3/8" end inside of it and sealed it up nice... didn't work out as planned as the coils cought on all the hoses and plug wires. was too much of a hassle so I tossed it.. I have a rubber tip for my air gun somewhere, I'll have to find it and try that.