A prosthetic or robot part, comprising: at least one phalange member pivotally coupled to a base at a pivot axis; and a drive assembly (502,504,506) to selectively move the phalange member about the pivot axis along a flexion/extension plane between an open position and a closed position, characterized in that said drive assembly comprises: a leadscrew selectively rotatable about a leadscrew axis by a motor; a leadscrew nut mounted on the leadscrew; and a leadscrew slider coupled to the phalange member and urged against the leadscrew nut by at least one spring urging the phalange member towards the open position; wherein, responsive to the leadscrew being rotated in a first rotational direction about the leadscrew axis, the leadscrew nut is moved in a first translational direction with respect to the leadscrew axis to urge the leadscrew slider in the first translational direction and rotate the phalange member about the pivot axis towards the closed position; and wherein, responsive to the leadscrew being rotated in a second rotational direction about the leadscrew axis, the leadscrew nut is moved in a second translational direction with respect to the leadscrew axis and the at least one spring urges the leadscrew slider to follow the leadscrew nut in the second translational direction and rotate the phalange member about the pivot axis towards the open position; and wherein, responsive to the phalange member being caused to rotate about the pivot axis towards the closed position by an external force, the leadscrew slider is moved in the first translational direction and away from the leadscrew nut. at least one phalange member pivotally coupled to a base at a pivot axis; and a drive assembly (502,504,506) to selectively move the phalange member about the pivot axis along a flexion/extension plane between an open position and a closed position, characterized in that said drive assembly comprises: a leadscrew selectively rotatable about a leadscrew axis by a motor; a leadscrew nut mounted on the leadscrew; and a leadscrew slider coupled to the phalange member and urged against the leadscrew nut by at least one spring urging the phalange member towards the open position; a leadscrew selectively rotatable about a leadscrew axis by a motor; a leadscrew nut mounted on the leadscrew; and a leadscrew slider coupled to the phalange member and urged against the leadscrew nut by at least one spring urging the phalange member towards the open position; wherein, responsive to the leadscrew being rotated in a first rotational direction about the leadscrew axis, the leadscrew nut is moved in a first translational direction with respect to the leadscrew axis to urge the leadscrew slider in the first translational direction and rotate the phalange member about the pivot axis towards the closed position; and wherein, responsive to the leadscrew being rotated in a second rotational direction about the leadscrew axis, the leadscrew nut is moved in a second translational direction with respect to the leadscrew axis and the at least one spring urges the leadscrew slider to follow the leadscrew nut in the second translational direction and rotate the phalange member about the pivot axis towards the open position; and wherein, responsive to the phalange member being caused to rotate about the pivot axis towards the closed position by an external force, the leadscrew slider is moved in the first translational direction and away from the leadscrew nut.