set screw

from The Century Dictionary.

• noun A screw, as in a cramp, screwed through one part tightly upon another, to bring pieces of wood, metal, etc., into close contact.
• noun 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.
• noun Specifically, a screw having a square head, the distance across the flats of the head being equal to the diameter of the screw.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun A screw with threads the entire length and no head. Typically, setscrews have a hex or slot drive recessed in the threaded length.
• noun 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.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun 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
• noun a screw that is used to adjust the tension on a spring