Murray breakers are intended for use in Murray and Crouse Hinds type load centers. These breakers are plug in style and are on a 1/2-Inch per pole format. See the wiring diagram on the load center for breaker type acceptance. The 1/2-Inch breakers will only fit in designed spaces within certain load centers. The wiring diagram will state if the MH-T breakers are accepted and will detail where they can be installed. 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.