Varivalve Straight 925006-00 is an adjustable Radiator Air Vent with 1/8″ pipe thread, designed for a single pipe steam heating/venting. The lab and in-field trials clearly show that a larger vent can vent a system more rapidly resulting in lowering operating pressure requirements. Phosphor bronze bellows of 925005-00 Radiator Air Vent provides a positive shut-off by closing and stopping the steam from escaping the radiator once heated by steam otherwise the steam will not fill the radiator.