Universal joints, or U-joints, are used to join shafts that must intersect at angles greater than those that can be accommodated by flexible couplings. They are generally classified by their motion transmission characteristic, which can be either constant velocity, nonconstant velocity, or near-constant velocity. U-joints can also be classified by their application: automotive, industrial, or mechanism.

U-joints fall into three categories:Automotive U-joints: Used for wheel drive shafts on cars, trucks, and off-highway vehicles, such as tractors, and earth-moving equipment.

Industrial U-joints: Used on vertical pumps, test stands, main rolling-mill drives and auxiliary equipment. Available in diameters to 40 in. capable of 15° misalignment, with torques to 15 million lb-in.

Mechanism U-joints: Used for cranking, steering, and others. Available from fractional to several hundred horsepower. Misalignments, 40° on a single unit and 80° on double units.