Flexible Couplings are one of the major types of couplings. They find use to connect two shafts, end-to-end in the same line to transmit power that is torque from one shaft to another, thereby causing both to rotate in unison, at the same rpm.

The purpose of a Elastic Coupling is to transmit torque from one piece of rotating equipment to another, while accepting at the same time a small amount of misalignment. Flexible coupling misalignment is expressed, as an order of magnitude, in thousandths of an inch. Actual misalignment, expressed in coupling terms, is angular in nature and expressed in angular units, that is, degrees. How much misalignment is a function of the coupling type and installation. An installation variable is the equipment movement due to the temperature changes taking place in the machines as they go from the non-operating state to operation. Some angular values will be used in the discussion of the various types, but, again, these are for reference only. Each application must be reviewed using the type of coupling selected and the specific design proposed by the vendor.