Sold as each. 1/2" male. Sweat connection. Uses a pressurized cushion of air to absorb the pressure spike. Dual O-ring piston separates the air cushion from the water system to ensure permanent protection from waterlogging. Easy to install. Arrestors can be installed vertically, horizontally or any angle in between. No access panels required. Manufacturer"s number: 660-S. Country of origin: United States. Distributed by Sioux Chief.