A hexagonal steel bar bent into an L, named after a trade name and used for every brand. The short leg gives leverage and the long leg gives reach, and ball-end versions allow angled entry at the cost of strength at the tip. Inch and metric sizes are close enough to fit loosely, a 5/32 in key in a 4 mm socket for example, and using the wrong system is the fastest way to round out a socket head.
Use the metric Allen key, the five-thirty-second fits sloppy in that 4 millimeter head and it'll round it out.
Cut the worn tip off a rounded key with a cutoff wheel and it grips like new.
Also heard as
- Allen wrench
- hex key
- hex wrench
Related terms
SHCS
Socket head cap screw: a round-headed, high-strength screw driven with a hex key into a tapped hole.
Rounded off
Describes a hex head, nut or socket recess whose corners have worn smooth so wrenches just slip.
Set screw
A headless screw, usually socket driven, whose point bears on a shaft to fix a pulley, collar or knob in place.