Cryogenic Stepper Motors are typically made in groups or families, the families are identified by the outer diameter or size of the square, these references are called frame sizes. In the American system, a 23 frame is a nominal 2.3 inches in diameter. For Cryogenic Stepper Motors less than one inch in diameter, the reference is typically known as a size. Herein is a list of the frame sizes offered by Empire Magnetics Inc. and some of the characteristics of the group that will allow you to select from them.