Universal joints, or u-joints are flexible mechanical connectors used to transmit rotary motion from one shaft to another shaft that is not in line with the first, or when alignment varies during service.  There are two types of universal joints, defined by their number of bending joints.  The first, the single joint, has only one bending aspect.  As a result, it is capable of operating at up to a 45-degree angle.  The second style is the double joint style.  By utilizing two bending joints, the double u-joint can operate at angles up to 90 degrees.  Additionally, it also accommodate parallel offset between 2 shafts with an operating angle of the central section from 0 to 45 degrees. Universal joints vary based on their material composition, hub type and the applications for which they are designed.  Steel is the most common material used, either in stainless form; or alloyed with other metals to handle greater torque and temperature.  Plastics and thermoplastics are often used in constructing universal joints, as this lends greater rust and corrosion resistance, as well as electrical and magnetic insulation in applications where this is required.