Do I need a 48-Frame or 56-Frame wet end?
How to be sure that your wet end is compatible with your motor, or vice versa?
Almost all spa pumps are manufactured in one of two standard frame sizes: 48-Frame and 56-Frame. When replacing your wet end or your motor, you should use an equivalent of the same size, so that the mounting holes on the motor and the wet end align.
The difference between a 48-Frame pump and a 56-Frame pump is in the distance between the mounting holes. The horizontal or vertical distance between the centres of adjacent bolts is 91 mm on a 48-Frame chassis, and 104 mm on a 56-Frame chassis (see diagrams, which correspond to the view from the front of a motor).