This Standard defines standard classes of flexible coupling potential unbalance@ one of which the user must select in order to meet the needs of his system. The balancing requirements for a flexible coupling depend upon the rotating system into which it is mounted. The balance classes are derived from consideration of the potential unbalance of the coupling. The AGMA method of computing coupling potential unbalance is provided. A guide is provided for balance class selection for purchasers who have not defined the coupling balancing requirements for their system. Application. This Standard is applicable to all flexible couplings@ unless otherwise specified by the individual manufacturer. It should be noted that a flexible Coupling is generally an assembly of several components having diametral clearance and eccentricities between the pilot surfaces. Exclusions. This Standard does not address the unbalance effects caused by such items as: (1) Shaft runout (2) Keys that protrude beyond the hub or shaft (3) Unfilled keyways or keyseats (4) Coupling mounting surface clearance (5) Non-homogeneous materials (6) Curved datum Additional Considerations. ISO Standard 1940/1@ Mechanical Vibration - Balance Quality Requirements of Rigid Rotors - Part 1@ Determination of Permissible Residual Unbalance@ may be used for balancing coupling components and assemblies in the balancing machine. However@ after the coupling is disassembled and reassembled either in the balancing machine or the rotor system@ significant potential unbalances are introduced. These potential unbalances@ as addressed in this Standard@ are primarily the result of: a. Balancing mounting fixture inaccuracies b. Displacement of coupling components with respect to the axis of rotation of the rotor system during disassembly and reassembly of the coupling.