Mueller Frost Proof Sillcock Anti-Siphon, Silver, Red, 1/2 In. Copper SWT x 1/2 In. MIP Prevents outside faucet freezing and protects against back siphoning A built-in backflow preventer checks siphoning back into the water supply The sill cock drains automatically upon water shut-off if the hose is removed or open 1/2" nominal copper sweat or 1/2" M.I.P. Import. No. 104-513: Type: Anti-Siphon Frost-Proof, Size: 1/2" Nominal Copper Sweat or 1/2", Finish: Chrome Plated, Material: Brass No. 104-515: Type: Anti-Siphon Frost-Proof, Size: 1/2" Nominal Copper Sweat or 1/2", Finish: Chrome Plated, Material: Brass No. 104-519: Type: Anti-Siphon Frost-Proof, Size: 1/2" Nominal Copper Sweat or 1/2", Finish: Chrome Plated, Material: Brass