An adaptor is used to couple a prime mover to an actuator. The adaptor includes a first portion that attaches to the prime mover and a second portion that attaches to the actuator. The outer surface of the first portion is defined by at least one flat portion connected by at least one arcuate portion. The second portion has a bore configured to accept the first portion, with an inner surface shaped to complement the outer surface of the first portion. A bore through the first portion accepts a drive shaft of the prime mover therethrough where the drive shaft is configured to engage the actuator.