A surgical device with a shaft having a distal end to which a surgical instrument is mountable and a proximal end equipped for handling the instrument, wherein the shaft is hollow and the surgical instrument is mountable on inserts that are longitudinally movable in the shaft parallel to the longitudinal axis and that are diametrically opposed to each other. The shaft comprises outer and inner tubes rotatable in opposite directions with respect to the longitudinal axis, and the inserts are coupled to the outer and inner tubes to convert rotational movement of the tubes into longitudinal movement of the inserts.