Push out to use and push back to lock. Wide Application: It is not just as a compression tester. There is 1pc 10" rubber hose and 2pcs aluminum adapters besides the combustion leak tester. The cylinder compression tester kit provides all the tools necessary for the compression check and leakage test of engine cylinders on most import and export petrol gasoline makes and models with M10, M12 or M14 spark plugs.