An actuator comprises an input shaft, a sliding collar arranged around the input shaft, and an output shaft. The input shaft, output shaft and sliding collar are arranged such that a torque applied to the input shaft can be transmitted via the sliding collar to the output shaft. The actuator comprises a torque-limiting device for limiting the transmission of torque between the input shaft and the output shaft if the torque exceeds a certain threshold. The torque-limiting device comprises one or more rolling elements arranged between the sliding collar and the input shaft to allow the sliding collar to move axially relative to the input shaft and engage with or disengage from the output shaft.