But they commonly leak. One cause of leakage is over or under tightening of the core. Most Schrader valve cores should be tightened to a torque of between 0.23 and 0.8 Nm.
Eliminating the guesswork which results in over or under tightening will reduce refrigerant leakage.
The photo shows an example of a simple torque tool. To use it simply tighten the core into the body until the tool clicks at its pre-set torque setting.
The use of the torque tool also ensures that the Schrader core depressor is at the correct height, so it is not fouled or depressed when a cap is fitted, but is depressed only by the pin in the gauge line.
A valve core comprises a machined component and a seal that screws into a separate valve body. The core seal is attached to a pin which is actuated when contacted by the depressor in your hose. An external seal on the core provides leak-free attachment between the core and body.