QO and QOB one, two and three pole thermal magnetic circuit breakers provide overcurrent protection and switching on ac and dc systems. These circuit breakers have an over center, trip free toggle mechanism with quick make, quick break action and positive handle indication. They also have VisiTrip trip indication, which provides a visual indication that the circuit breaker has tripped and interrupted the circuit. This mechanical interlock attachment kit is for interlocking the handles of two 2P or one 2P and one 1P QO and Q1 circuit breakers. Circuit breakers are to be mounted side by side so that only one circuit breaker can be ON at a time. Can't be used with QOU breakers.