Valve clearance is easy to adjust on all push rod engines or OHC engines with top adjustment. Clik-adjust makes the job easier and absolutely precise. This essential clearance adjustment ensures the valves (inlet and outlet) open and close correctly resulting in better engine performance. Adjusts tappets preciselyMicro adjustment No need to use feeler gauge after its set up. Suits all push rod valve engines and OHC engines with Flat head top adjustments screws.1/2"D for any size lock nut.