inbus

Inbus is a term used to describe a type of screw or bolt drive that features an internal hexagonal recess. In German-speaking contexts, Inbus commonly refers to the Innensechskant (internal hex) drive and its accompanying hex keys, though the term is sometimes used more broadly as a generic name for hex socket screws. The concept is widely known in English as the hex socket or Allen drive.

The drive is engaged with a hex key or hex bit, which fits into the six-sided recess to turn the fastener. This design allows for high torque transfer in a compact, recessed profile, enabling the fastener head to sit flush or below the surface in many applications.

Inbus screw and bolt systems are standardized within various DIN and ISO standards for socket screws and bolts. Common forms include socket head cap screws (often with a cylindrical head), countersunk socket screws (flat head), and button head socket screws. These fasteners are used across machinery, automotive, furniture, and bicycle applications, among others, particularly where a low-profile or clean appearance is required.

Advantages of the Inbus/hex socket drive include reduced cam-out risk compared with some slotted drives and the ability to achieve strong fastening with the right tooling. Disadvantages include the need for a compatible hex key or bit, potential rounding of the hex recess if over-torqued or damaged, and reduced accessibility in tight or recessed spaces.

Etymology: the German term Innensechskant is standard, while Inbus is a colloquial or historical label that has persisted in some markets. In English contexts, the terms hex socket or Allen drive are more common.