Frames" refers to the size of your Motor. All main spa motors have either 48 or 56 frames. 48 frame motors are 5.5" in diameter. 56 frame pump motors are typically 6.5" in diameter. You can also determine the frame size from the bolt spacing- the 48 frame is 3-5/8" and the 56 frame is 4-1/8."

To determine the size of the plumbing, measure from outside thread to outside thread.

56 frame spa wet ends can have one of two designations - 6.1 or 6.3. The difference is the measurement between the top two thru-bolts. 6.1 wet ends measure 4" and 6.3 wet ends measure 4-1/8"