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 4-1/4."

To determine the size of the plumbing, measure from outside thread to outside thread.
 If it measures 2 3/8 it is 1 1/2 inch.
 If it measures approx 3 inches, it is 2 inch.

We are asked how large of a pump can I put on my spa?   Well, 1.5 inch plumbing  2.0hp.  2 inch plumbing 5hp.

RULE of THUMB; 10 - 15 jets - 1.5 -2 hp, 15 - 20 jets - 3hp, 20 - 25 jets -  4hp ( This is WATER no Air jets. ) You do not have to have the same size pump with multiple pump systems. 2 & 3, 2 & 4, 3 & 5 etc based on your performance and jet requirements.