A switch actuator mechanism, for example for use with a circuit breaker, includes a rocker which has first and second rocker members which are hinged together. The rocker members have flat front faces which are movable between a condition in which they lie flat in the same plane, and a second position in which the faces are inclined relative to one another, with one rocker member standing proud of the housing of the switch or circuit breaker. Fingers on one of the rocker members engage a link of the circuit breaker mechanism to open or close its contacts. A spring loaded latching mechanism locks the rocker members alternately in their first and second conditions with successive operations of the mechanism.