This Harmony XB4, metal blanking plug is compatible with Harmony XB4, pushbuttons with flush push. This metal blanking plugis designed as an option to fit with your pushbutton units when no function is needed for machine to operate. It is compatible with standard 22mm XB4 control and signaling unitsMetal bezel. It is designed to fit in a standard 22mm cutout, ensuring compatibility when installing in pre-existing machinery.