For those of you with powerful pumps. This pressure gauge mounts inline and measures in PSI. Lower powered pumps might not register on the dial because it Reads from 0-15 PSI. Good way to tell if you have good flow (lower number) or restricted flow (higher number). Also as heat builds so does the pressure. It comes all assembled with 1/2" or 3/8" Size barbs. So if you know you have a powerful system, this would be a great addition.