Setscrews

Setscrews, or grub screws, are fasteners designed to secure an object within or against another object without a protruding head. Most are fully threaded along their length and are tightened by turning an internal drive, such as a hex socket (Allen), Torx, or a slotted drive. Because there is no external head, the screw bears directly on the mating surfaces as it is tightened.

The defining feature of a setscrew is its point, which can be flat, cone, cup, dog, or serrated. The point design influences how the screw contacts the surface or shaft and can affect grip, surface marking, and the distribution of clamping force. Setscrews are used to locate, lock, or hold parts such as pulleys, gears, collars, and machine components onto a shaft or within a bore.

Materials and finishes vary. Common materials include alloy steel (often hardened and tempered), stainless steel, and brass. Finishes include zinc plating, black oxide, or plain finishes. Sizes cover metric ranges (for example M4 to M16) and imperial sizes (such as 6-32, 8-32, 10-24), with various drive styles available.

Common applications include securing components on shafts, adjusting stops, or mounting components in compact assemblies where a traditional head would be impractical. For preventing loosening in critical applications, thread-locking compounds or locking setscrews are sometimes employed, and care should be taken to avoid over-tightening which can damage threads or deform surfaces.