Carbon Steel Metric Allen Keys-Hex Wrench-Hexagon Key 0.9mm - 4mm All Sizes

Measure the width across the flats of the hex socket (the opening in the bolt head or set screw). This measurement in millimeters corresponds directly to the hex key size you need. For example, a socket that measures 2 mm across the flats requires a 2 mm hex key. If you are unsure, start with the next size down and work up — a key that is too large will not enter the socket, while one that is too small will slip and damage the drive.

These carbon steel hex keys are designed for standard torque requirements on metric socket-head cap screws and set screws in the 0.9–4 mm range. For sub-2 mm sizes in particular, the fasteners themselves are the limiting factor — apply only the torque specified by the fastener manufacturer to avoid stripping the socket. They are not intended for impact driver use or for fasteners requiring calibrated torque values in safety-critical assemblies.

The Black finish is a black oxide coating that provides a degree of corrosion inhibition in dry to moderately humid environments and reduces light reflection, which can be useful in low-light workspaces. The Silver (bright) finish is an uncoated or lightly treated surface that makes the key easier to spot in a cluttered tool tray. Both finishes are available across the same size range; the choice is primarily practical and visual rather than functional.

No. These are metric hex keys sized in millimeters and are not interchangeable with SAE (inch) hex fasteners. While some metric and inch sizes are close in dimension (for example, 3/32" ≈ 2.38 mm), using a metric key in an inch socket — or vice versa — risks rounding out the drive. Always use the correct standard for your fasteners.

Carbon steel hex keys can drive stainless steel fasteners under normal torque conditions. However, for hardened or high-tensile fasteners (Grade 12.9 or equivalent), a chrome-vanadium or S2 steel hex key is generally recommended for better durability. For occasional use on stainless fasteners at moderate torque, these keys perform adequately; for repeated heavy-duty use, consider an alloy steel alternative.

For a general-purpose toolkit, ordering 5–10 pieces of the most commonly used sizes (typically 2 mm, 2.5 mm, and 3 mm) provides a practical buffer against loss or wear. If you are assembling a repair kit for a specific product line — such as bicycles or flat-pack furniture — ordering 20–30 pieces of the sizes specified in your assembly instructions ensures you have stock for multiple units. The 50-piece option is suited for small production runs or resale kits.

"Side" refers to the hex key size — the width across the flats of the hexagonal cross-section, which must match your fastener's socket. "H" is the length of the short arm of the L-shape, used when you need more torque in a confined space. "L" is the length of the long arm, used for reach into deep or recessed sockets. For example, "2 × 17 × 50 mm" means a 2 mm hex key with a 17 mm short arm and a 50 mm long arm.