Couplings connect rotating shafts to transmit power, typically found within the drivetrain – from the transmission to the axles, or between engine components. These components dampen vibration, accommodate minor misalignment, and protect components from torsional shock. Designs range from single-piece solid couplings to multi-piece flexible types utilizing elastomers, gears, or fluid. Key specifications include bore diameter, shaft acceptance criteria, torque capacity, and operating speed limits. Materials commonly include steel alloys, aluminum, and specialized polymers selected for durability and performance characteristics.