Allen Key (Hex Key)

ALLEN KEY (HEX KEY)

An Allen key (or hex key) is an L-shaped tool used to drive fasteners with a hexagonal socket (Allen bolts). The vast majority of fasteners on modern bicycles use hex socket heads, including stem bolts, handlebar clamp bolts, saddle clamp bolts, and brake caliper bolts.

Carrying a multi-tool with various sizes of Allen keys (commonly 3mm, 4mm, 5mm, and 6mm) is essential on every bicycle ride. It allows for roadside repairs and adjustments to most components on the bicycle.