[1376]. Earth screw, screw pile, screw mooring, earth borer. See [No. 530].
[1377]. Fixed screw, with hand wheel to revolve the nut, the screw having no rotation.
[1378]. Conical screw; used for chucks, &c. With two, three, or more sliding jaws chased to fit the conical thread.
[1379] & [1380]. Differential screws. One fixed, the other revolving, impart a motion equal to the difference of pitch of the two screws (see [Section 31]). See [No. 1430].
[1381]. Screw, with half nut; the bearings of the screw being fixed act as a fulcrum for the motion of the half nut, which may be attached to any sliding device; employed for jaw chucks.
[1382]. Screw and worm gear, used for screw jacks, &c. The worm gears with a worm wheel having a central nut running on the main screw.
[1383]. Mutilated screw and nut. In one position the nut can slide on the screw, and a partial turn locks it. Used for instantaneous grip vices, &c.
[1384]. Spiral worm for three or four jaw chucks, expanding devices, &c.
See [Sections 28] and [36].