Square head set screws are a fully-threaded stud-like fastener with a square head at one end and a cup-shaped indentation on the other end. The thin edge of the cup digs into the mating surface for holding power and the square head allows for hand or wrench tightening. Square head set screws are made from quenched and tempured plain finish alloy steel and have a minimum tensile strength of 170,000 PSI.