Passfeder

Passfeder is a term used in German-speaking engineering to describe a class of locking or locating elements designed to secure two components—typically a shaft and a hub—together while accommodating dimensional tolerances. The exact design varies by application, but passfeder elements generally combine a shaping mechanism with a spring or preload feature that creates axial retention and, in some variants, limited radial or angular compliance. The function is to transmit torque and locate components along the shaft axis, while enabling assembly and disassembly with controlled force.

Construction and variants: Devices in this family may consist of a groove or pocket in one component and a spring-loaded latch, pin, or wedge that engages the groove under preload. Some variants use coil springs, wave springs, or elastomer elements to maintain contact pressure. Materials are typically steel or stainless steel; coatings may provide wear resistance. Axial preload can be adjusted by shims, screws, or by selecting spring stiffness. The exact geometry is chosen to balance ease of assembly, torque capacity, and tolerance compensation.

Applications: Passfeder elements appear in machine tools, automotive transmissions, servo and stepper motor assemblies, gearboxes, and other equipment requiring repeatable axial positioning and torque transmission with tolerance compensation. They are used when a conventional key or dowel arrangement would be insufficient or too rigid for the application’s tolerance stack.

Etymology and terminology: The name derives from German passgenau (“precisely fitting”) and Feder (“spring”). In English-language literature the exact concept is described by a variety of terms and is not universally standardized; similar functions are achieved by keys, dowel pins, or clamping devices depending on context.

See also: Key (machine element), Dowel pin, Clamping collar, Torque transmission devices, Alignment pin.