The coupling carries drive torque from the motor to the airend and absorbs the small misalignment that no rigid connection could survive. Its flexible element takes the torsional shock of every start, so it is the part that cracks and perishes while the metal hubs stay serviceable.
Check the bore, the keyway and the element profile against the old coupling, and confirm the element hardness if the machine has been rebuilt. Align the shafts after fitting; a new element will not survive the misalignment that destroyed the old one.
