The Woodford NIDEL® Model 34HA and 37HA anti-siphon vacuum breaker are designed to protect Woodford hose connections from contamination. Uses include laundry tubs utility sinks boiler room and outside hose bibbs. Models 34HA 37HA Vacuum Breakers and 50HA Backflow Preventer have 3/4" rough thread. NOTICE:These products as with all 1011 1019 1052 and 1053 ASSE listed devices are not to be subjected to continuous water pressure. Replacement is recommended every 3-5 years. After use turn device to open drain vents or faucet may freeze and burst.