This piece allows for the quick detachment of the a switch mount without losing the switch position. External threads at either end connect to stems or other internally threaded STEM components. Three counter clockwise turns of the black rubber sleeve on the Quick Release loosens the body enough for it to be twisted and lightly pulled free from the socket. Or it can be rotated 120 degrees out of the way. Re-installation is just placing the switch mount back into the socket of the Quick Release with a twisting motion until the body clicks into place. A further rotating motion may be necessary to get the switch mount to into the correct position. Now re-tightening the black rubber sleeve in a clockwise position completes the re-attachment of the switch mount.
For more detailed information on the Quick Release GO HERE