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 retaining kit is a QO2DTI mechanical interlock attachment with retaining kits for securing two adjacent back-fed circuit breakers. This attachment is used in dual power supply applications. It can be used with two 2P or one 2P and one 1P QO circuit breakers. Breakers and attachments are to be in a QO816L100 load center.