A primary consideration in the selection of a switch is the number of circuits required for an application, or how many things are being turned on or off at one time. Switches are specified by poles and throws, where a pole is one circuit and a throw is an ON position. Therefore, a single pole single throw switch, abbreviated SPST, has one off/on position. An SPDT switch is a single pole double throw switch with two on positions, a DPST is a double pole single throw switch, and a DPDT switch is double pole double throw.