Prier 4 in. L 1/2 in. MPT x SWT, 478-04 Series Heavy Duty, Frost-Proof, Anti-Siphon Sillcock is connected to the supply piping in the heated portion of the structure, eliminating the possibility of freezing. The Prier 478 Series features an anti-siphon vacuum breaker and backflow preventer with a solid brass body and seat. Designed to be easy to install and maintain. Built to last the life of your plumbing system.