The Hoffman Steam Unit Heater Vent No. 78 is a 3/4" x 1/2" unit designed to allow for venting in heating systems. With a maximum pressure capacity of 150 psi, this product is suitable for use in various industrial and HVAC applications. Manufactured by Hoffman, a trusted brand in the industry, this vent unit ensures efficient and reliable ventilation for steam heating systems. Item is untested. Comes with original box and tag. Looks to be in working order but I don't know if it's ever been installed.