That fitting is installed between the hot and cold supply lines at a single location/fixture in the house, usually the farthest away from the heater. Then, a compatible tankless heater can use a pump to push hot water out while pulling the cold water back in through the cold supply line - so no extra recirculating pipe has to be installed. You trigger the recirculation with a switch at the fixture, on a schedule, or with an app/smart home device.

And you need to buy 2 if you don’t want to rebound!

They look great! I guess I’ll be the one to point out, it’s spelled ‘amok’

Google drive does this even more, and every month or so they make the ‘show file location’ harder to find

By my napkin math, from 32 billion km away, a 2deg error means Voyager 2 is pointing to a spot 1.12 billion km away from Earth (at right angles). That’s roughly the distance from Earth to Saturn 😅