An injector head for feeding a tool string support member downhole is described. The injector head includes a first gripping device and a second gripping device. The first and second gripping devices are adapted to grip a tool string support member passing through an injector head passageway. The injector head further includes an actuator movable between a first position and a second position wherein, movement of the actuator between the first and second positions moves at least a portion of both of the first and second gripping devices towards or away from a passageway longitudinal axis.