Standard on Woodford Models C22 B22 25 27 and 30 with 1 1/8-in - 18 special threads X 3/4-in hose threads. 

The first ASSE 1052 Approved automatic draining high-flow double-check backflow preventer. When a hose is removed from a Model 50 equipped wall faucet or yard hydrant two linked but independent check valves automatically move as one to open a path through the valve allowing water to drain completely and prevent freezing.

Used in the following models: B22, C22, 25, 27 & 30.