A cylinder, or a cylindrical perforation, having a
   continuous rib, called the thread, winding round it spirally at a
   constant inclination, so as to leave a continuous spiral groove between
   one turn and the next, -- used chiefly for producing, when revolved,
   motion or pressure in the direction of its axis, by the sliding of the
   threads of the cylinder in the grooves between the threads of the
   perforation adapted to it, the former being distinguished as the
   external, or male screw, or, more usually the screw; the latter as the
   internal, or female screw, or, more usually, the nut.