The 1.5 inch standard pump union is a universal pump union used for complete assembly of your replacement pump. Should fit any 1.5 inch end on most pumps.
The 2 inch Pump Split Nut is used as a replacement for the pump union that would need to be re-plumbed. You can cut off the old pump union and replace with this split nut. This comes with the 2 screws that screw and hold it together.
The Pump Pad is your key to a quieter running spa/hot tub. Mount your pump on the pad to prevent transmission of the noise and vibration from the motor in your pump. Works well with pumps on most models.