Hoffman 4A Convector Non-Vacuum Straight Steam Vent, 3/4 X 1/2 Inch, Fnpt X Mnpt, 10 Psi, Steel Hoffman 4A Convector Non-Vacuum Straight Steam Vent Is Made Of Steel That Provides Strength And Long Lasting Durability. Vent With Single Non-Adjustable Port Supports 1/2 Inch Fnpt X 3/4 Inch Mnpt End Connection And Has Pressure Rating Of 10 Psi. It Offers Easy Installation Of 6-10 Inch Above Horizontal Return And 18 Inch Above The Boiler Water Line. Float-Type Thermostatic Vent Measuring 3/4 Inch X 1/2 Inch Operates At A Maximum Operating Pressure Of 2 Psig And Is Suitable For Residential Or Small One/Two-Pipe Systems.