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.
Specifically, a kind of nail with a spiral thread and a head with a nick to receive the end of the screw-driver. Screws are much used to hold together pieces of wood or to fasten something; -- called also wood screws, and screw nails. See also Screw bolt, below.
A straight line in space with which a definite linear magnitude termed the pitch is associated (cf. 5th Pitch, 10 (b)). It is used to express the displacement of a rigid body, which may always be made to consist of a rotation about an axis combined with a translation parallel to that axis.