Metric Short Arm Allen Keys-Hex Wrench-Hexagon Key 0.7mm - 8mm All Sizes

Measure the width across the flats of the hex socket in your fastener using a caliper or a go/no-go gauge. The key size must match exactly — a 3 mm key will not seat correctly in a 3.5 mm socket and can round out the drive. When in doubt, start with the next size down and work up until the key seats without play.

The short arm is the side you insert into the fastener; the long arm is the handle you turn. On a short arm Allen key, the inserted leg is shorter than on a standard key, allowing access to fasteners recessed inside narrow channels or close to obstructions. The trade-off is less mechanical advantage, so short arm keys are best for lower-torque applications.

Carbon steel hex keys handle the torque ranges typical for M1–M8 metric fasteners in furniture, bicycles, and light machinery. For very high-torque industrial fasteners (e.g., structural bolts above M8), a ball-end or T-handle hex key with a longer arm provides better leverage. Always apply torque gradually and stop if you feel the key beginning to twist or the socket beginning to round.

Carbon steel can develop surface oxidation if stored in a damp environment. To extend service life, wipe keys dry after use, apply a light coat of machine oil periodically, and store them in a dry toolbox or roll. For consistently wet environments (marine, outdoor), consider stainless steel hex keys instead.

No. Metric and SAE hex sizes are not interchangeable. While some metric sizes are close in dimension to certain SAE sizes (e.g., 5 mm ≈ 13/64 in), using a metric key in an SAE socket — or vice versa — risks rounding the drive. Always match the key system (metric or SAE) to the fastener system used in your equipment.

Most road and mountain bike derailleur limit screws use a 2 mm or 2.5 mm hex key. Brake caliper mounting bolts commonly require 5 mm or 6 mm. Stem and handlebar clamp bolts are typically 4 mm or 5 mm. If you are unsure, ordering a multi-quantity pack of the 2 mm, 2.5 mm, 4 mm, and 5 mm sizes covers the majority of bicycle hex fasteners.

Yes. Each size is listed as a separate variant. Select the size and packing quantity you need, add it to your cart, then return to this page to select additional sizes. Repeat for each size required. All items will ship together in a single order.