The 641 is an air pressure switch with 1.2 Kohm resistance on a connection PCB in a plastic housing with swivel with anti-kink grommet on the lid and air hose. A slack cable switch and wicket door contact can also be connected to the connection board via screw connectors. An optional spiral cable can be fed through the gland with anti-kink grommet on the lid and connected to the connection board via screw connectors.