SCREW

n. Skru. Gr., eAif, Kox^i'at. Lat., cochlea. Fr., vis. Ger., Schraube. A cylindrical rod round which there winds, at a constant angle to its axis, a continuous raised part, called the thread of the s. This fits into (sometimes making for itself) a corresponding spiral depre ion in a socket (called the nut) or canal, and the s., as it is turned, moves slowly forward or backward in the direction of its length. The uniform distance that separates contiguous turns of the thread is called the pitch of the s. [a, 48.] Micrometer s. Ger., Mikrometer-Schraube. A s. with a very slight pitch for moving some part of a machine a short distance and very slowly, as in the fine adjustment of microscopes or for measuring very minute distances or dimensions. The head of the s. is usually graduated, and the distance traversed by any part of a revolution may thus be read off at once. [J, 210.] Oral s. A large tapering hard-rubber or bone s. for introducing between the teeth to separate the jaws. [E.] Pan coast's s. A gimlet-like instrument for drilling the fragments in ununited fracture. [E.] S. hook. Fr., vis-crochet. Ger.. Schraubhaken. Of Elsberg, an instrument, something like a corkscrew, for the removal of foreign bodies from the ear. [F.] [s. 464]