This part is a Vacuum Switch like you will find on some  Cal Spas in the suction side of the pump.

Specs V4001P-DX Replacement, 21A, 1/8"mpt.

For a switch like the original click this link: PresAirTrol Style Vacuum Switch

This is a normally open switch and is closed when there is too much vacuum on the suction side of the pump. For instance a person being held down to a suction return in the tub.. When enacted the closed circuit will stop the pump from running and allow the person to move..