Couplings connect rotating shafts in order to transfer motion, power, and torque. Types of couplings include rigid, jaw, geared, chain, and fluid. A rigid coupling provides firm connection with very little flexibility, ensuring that the shafts are securely held. The rigidity of the coupling requires that the shafts be in alignment with minimal deviation. Variations of rigid couplings are sleeve, flanged, and clamped. Jaw couplings dampen vibrations and work well with high rpm. Jaw couplings are formed by two hubs and an insert called a spider. Jaw couplings must have minimal misalignment to perform optimally. Applications for jaw couplings include compressors, cranes, and gas engines. Geared couplings transfer torque when shafts are not aligned. Some geared couplings are flexible, allowing for shaft deviation, while others require more rigidity. Rigid gear couplings comprise solely of two hubs, while flexible couplings include a sleeve. Geared couplings are used in rolling mills, gearboxes, and motors. Chain couplings contain two sprockets, chain, and a cover. They compensate for slight misalignments but operate at slow speeds. They are often placed at the end of a reducer or motor. Fluid couplings use water or hydraulic oil to transfer torque and power. Fluid couplings provide the ability to control the acceleration, torque, load sharing, and speed. They consist of a pump wheel and two bladed wheels submerged in liquid. These parts experience minimal wear due to the fact that there is no physical contact between the coupling and shaft. Applications for fluid couplings include power generation, mining, and material processing.