This is a Washing Machine Mini-Rester Water Hammer Arrester (660-H) used to stop banging pipes by utilizing a pressurized cushion of air to absorb water pressure spikes - it is primarily used to prevent pressure spikes in the water lines leading to washing machines and other compatible appliances. It also stops in-the-wall pipe banging and rattling which reduces overall strain on plumbing systems. It has a 3/4" female swivel hose thread x 3/4" male hose thread tee. It is compatible for use with both hot and cold water pipes.
The Sioux Chief 660-H Water Hammer Arrester replaces the need for air risers. It generally requires 2 per machine (1 for hot water, 1 for cold water). It can be installed vertically, horizontally, or any angle in between. No access panels are required to use this part. It includes a washer. It was manufactured in the USA and is also known by part number 660H.