Murray breakers are intended for use in Murray and Crouse Hinds type load centers. These breakers are plug in style and are on a 1-Inch format. Single pole breakers are 1-Inch , double pole are 2-Inch , three pole are 3-Inch , and 4 pole are 4-Inch wide. See the wiring diagram on the load center for breaker type acceptance. Murray strongly recommends against the use of "used" breakers. The installation of used breakers in a Murray panel will void the warranty on the panel. Murray does not sell used breakers and has not approved any 3rd party sellers to do so.