A Hirth joint, sometimes called a Hirth coupling, is a precision face-to-face connection used to transmit torque while maintaining accurate concentric alignment between rotating components. Each mating face is machined with a series of radial serrations that form tapered teeth, typically arranged in a circular pattern around the shaft axis. When the two faces are pressed together—often by a central bolt or clamping nut—the interlocking teeth engage, creating a rigid, self-centering interface capable of carrying substantial torque without relying on friction alone. Because the teeth are equally spaced, the joint also provides repeatable angular indexing, allowing parts to be assembled in defined rotational positions. Hirth joints are common in high-performance applications such as turbine rotors, machine tool spindles, and modular fixturing systems where both torque transmission and positional accuracy are critical.