A hex key is a simple tool that fits into the hexagonal recess of a fastener. The typical design is an L-shaped steel bar that matches the shape of the recess.
Typical applications
- Hex keys and hex drivers are used to turn fasteners that have a matching hexagonal socket. They are not suitable for fasteners with other recess shapes.
Advantages
- Available formats include L‑shaped keys, folding sets, T‑handled drivers and socket forms. These provide format choices; no comparative access, force or speed advantage is established.
Specifications to check
- Key size is measured across the flats of the hexagonal stock. Metric and imperial sizes are available. Identify the specified profile and size before choosing.
Limitations
- This guide does not provide tightening torque, insulation rating, or suitability for a specific assembly. If fastener specifications are unknown, the selection remains unresolved.
Buying considerations
When choosing a hex key, first check the assembly specifications and compare the required sizes. Avoid picking a tool that only looks close; it may not fit correctly. No brand is preferred or ranked.
Safety & limits
- Inspect the hex key for defects before use and set defective tools aside for repair or replacement. Avoid excessive force. Keep tools clean, dry and properly stored.
Sources & further reading
These links document the information used in this article. Manufacturer specifications and source research are not hands-on test results or an endorsement of a purchase.
- TRU Open Press: hand-tool definitions
Reference checked 2026-10-28 - CCOHS: general hand-tool guidance
Reference checked 2026-10-28