A medical instrument comprises a tubular introducer member, an operative element, an elongate shifter connected at a distal end to the operative element, a handle, at least one stop component, and an override. The shifter and the operative element are movable relative to the tubular member, while the first part of the handle is fixed to a proximal end of the tubular member and the second part of the handle is fixed to a proximal end of the shifter. The stop component is disposed on the first part or second part to limit relative motion of the first part and the second part and concomitantly to stop travel of the operative element at a predetermined location relative to a distal end of the tubular member. The override enables a user to override or passivate the stop component and thereby permit travel of the operative element past the predetermined location.