This cylinder leak-down tester gauges leak-down tests more accurately than standard compression tests! Pressurized air is supplied to each cylinder and in moments displays a rate of leakage measure from 0 to 100%. The leak tester includes 12mm x 14mm spark plug adapters; Quick-connect/disconnect 3/8 in. diameter hose; Easy-to-adjust air regulator;Easy-to-read 2-1/2 in. input pressure gauge for proper leakage test setup and accurate results.