Inbusschlüssel

Inbusschlüssel, in English often called hex key or Allen key, is a hand tool used to drive screws or bolts that have hexagonal sockets in their heads. It is typically an L-shaped rod with a hexagonal cross-section, allowing the user to fit the outer corners of the screw head and apply torque. Ball-end variations let the key enter at oblique angles; there are also straight or T-handle versions for different applications.

Sizes are expressed in metric millimeters or imperial inches. Common metric sizes range from 2 mm to 10 mm, while common imperial sizes range from 1/16 inch to 3/8 inch. Sets may include multiple sizes in a single holder. The length of the arms and the thickness of the material affect leverage and fit in tight spaces.

Manufacture typically uses hardened tool steel such as chrome vanadium, sometimes stainless steel, with finishes such as zinc plating or black oxide to resist corrosion. The tool is designed to engage the hex socket to avoid rounding the corners of the screw head.

Historically, the hex drive was popularized in the early 20th century by the Allen Manufacturing Company, giving rise to the widely used term “Allen key” in many regions. Today the Inbusschlüssel is common in furniture assembly, bicycle maintenance, automotive repair, and various mechanical and electronics applications where hex socket fasteners are used.