Allen wrenches, also called "hex keys," start as large pieces of steel alloy known as billet. These 50- to 80-lb. blocks are loaded into a powerful hydraulic press that squeezes the malleable metal through a small opening, creating a long, rod-like piece. This rod is then attached to an empty spool that stretches and winds it into a coil of steel wire. The diameter or gauge of the wire used depends on the target wrench size. Once complete, the spool is loaded into a new machine that slowly feeds the wire through a pair of rollers which straighten it out completely. The straightened wire is then cut into long pieces and loaded into a narrow tube. One end of the tube is capped with a disk that has a hexagon cut from the center. Known as a die, this special disk is responsible for given an Allen wrench its trademark six-edged shape.
Once the wire is loaded into the tube, a hydraulic piston at the opposite end pushes against the wire, squeezing it through the die's hexagonal opening to create a hexagonal cross-section. For small gauges, only a single die is used. For larger gauges, the wire is forced through a series of dies that create the hexagonal cross-section more gradually.
Bending and Heat Treatment
Upon exiting the extrusion die, the hexagonal wire is cut into short, standard-length pieces. These pieces each travel through a special corner-shaped hydraulic press that stamps a 90-degree bend in them. Once it has its classic L-shape, the Allen wrench enters a furnace for heat treatment. Exposed to extreme temperatures for hours, the steel becomes tempered and hard. Tempered Allen wrenches are cleaned, degreased and submerged into a 285-degree F bath of alkaline salts. This causes a protective coating of black oxide (Fe3O4) to form on the surface.
Ball Head Hex Keys
For security purposes, certain companies order specially made tools called "ball head" hex keys for their machinery. Unlike a basic Allen wrench, ball head hex keys have a depression around the entire circumference of the shaft just above the head.
To create this shape, an extruded and bent Allen wrench is grasped by a robotic arm that presses the side against a spinning, round-edged grinding wheel. The arm aligns each of the six flat edges so that it is perpendicular to the grinding wheel. The piece is then lowered into the wheel until the desired amount has been ground away. The piece is lifted and rotated in preparation for grinding the next five sides. Once complete, the ball-headed hex key goes through the same tempering and oxide coating as a regular Allen wrench.