This gauge is made with an adjustable valve head depressor. The gauge is preset to work on Leafield and Halkey-Roberts (Red Paddle Co) configured valves.
To adjust for other valves, the screw in the gauge can be rotated to extend or retract.
For this gauge to function on Summit, Halkey-Roberts, Innova and similar valves, you must leave the included adaptor securely affixed to lower end of the gauge. For Leafield and Military valves, the adaptor must be removed.