set screw

Century Dictionary and Cyclopedia

1. n. A screw, as in a cramp, screwed through one part tightly upon another, to bring pieces of wood, metal, etc., into close contact.
2. n. A screw used to fix a pulley, collar, or other detachable part to a shaft, or to some other part of a machine, by screwing through the detachable part and bearing against the part to which it is to be fastened. Such screws have usually pointed or cup-shaped ends, which bite into the metal.
3. n. Specifically, a screw having a square head, the distance across the flats of the head being equal to the diameter of the screw.

Wiktionary

1. n. A screw with threads the entire length and no head. Typically, setscrews have a hex or slot drive recessed in the threaded length.
2. n. Any screw used to hold or adjust a setting. Frequently a setscrew (1), but may also refer to any other machine screw or thumb screw used for the purpose of setting.

GNU Webster's 1913

1. adj. (Mach.) a screw, sometimes cupped or printed at one end, and screwed through one part, as of a machine, tightly upon another part, to prevent the one from slipping upon the other.

WordNet 3.0

1. n. a screw (often without a head) that fits into the boss or hub of a wheel or cam etc. and prevents motion of the part relative to the shaft on which it is mounted
2. n. a screw that is used to adjust the tension on a spring