Rigid couplings connect rotating members such as shafts and transmit torque and motion. Most rigid couplings are made of aluminum, steel, or stainless steel. There are several basic types of products. One-piece set screw devices are solid, O-shaped couplings that attach to shafts with set screws. One-piece clamp couplings are solid, C-shaped devices with a split that is closed with tightening screws. Two-piece clamps are split axially into two pieces, each of which is closed onto the shaft with tightening screws. Multi-screw couplings are commonly available. Typically, all of the screws are inserted from the same direction. Shrink discs are rigid couplings with two external rings that tighten together axially and exert inward force on a third ring via tapered surfaces. This closes the inner ring onto the shafts and provides a secure connection. Rigid couplings with keyways include keys that can be used to stop the rotation of the shaft couplings. 

Mechanical properties for rigid couplings include rated torque, rated speed, torsional stiffness, and backlash. Rated torque is the maximum service torque for which the device is rated.  Rated speed is the maximum rated rotational speed of the coupling. Stiffness is expressed in torque per units of angular deformation (degrees). Backlash, the rotational position loss due to a change, is also measured in degrees. Important dimensions to consider include bore diameter, coupling diameter, coupling length, and design units. Bore diameter is the internal diameter for mating to the shaft-end. Coupling diameter is the outside diameter (OD), a measurement which includes the housing. Design units are English measurements such as inches (in) or metric measurements such as centimeters (cm). For rigid couplings with one or more keyways, keyway width is an additional consideration.  

Alignment and motion parameters to consider when specifying rigid couplings include angular misalignment tolerance, parallel misalignment tolerance, and axial motion allowed. Angular misalignment tolerance is the maximum angular misalignment between coupled shafts that rigid couplings can accommodate.  Similarly, parallel misalignment tolerance is the maximum parallel offset between shafts that rigid couplings can accommodate. Axial motion allowed refers to the relative axial motion allowed by the coupler between two shafts.