The Leakdown Tester pinpoints internal engine problems before you tear down your engine. Checks the condition of rings, valves, cylinder heads and walls, and head gaskets. Pressurize the tester with your compressed air (50-150 p.s.i.), then screw the flex hose into a spark plug hole. Color-coded gauge (2 1/4in. dia. face) indicates the percentage of leakdown. Instructions guide you toward possible causes. Rubber connecting hose (12 in.) and 14/18mm plug thread adapters included.