one of the six mechanical powers, is a cylinder cut into several concave surfaces, or rather a channel or groove made in a cylinder, by carrying on two spiral plains the whole length of the screw, in such a manner that they may be always equally inclined to the axis of the cylinder in their whole progress, and also inclined to the base of it in the same angle. See Mechanics, p. 66, No. 131.

Archimedes's Screw. See Hydrodynamics, No. 328.

Endless or Perpetual Screw, one so fitted in a compound machine as to turn a dented wheel; so called because it may be turned for ever without coming to an end. See Mechanics, p. 67, No. 135.