Product Description
This fitting should always be mounted in the vertical upright position (shown below). In this condition, air flow is permitted to move through the unit in both directions (in and out). 
However, when the fitting rotates more than 90 degrees, it becomes a shut-off valve not allowing any flow to pass through. 
This part was designed to be compatible with Radium Engineering P/N: 18-0042 AIR FILTER, 0.75IN ID (shown above). This combination is most commonly used with engine (or oil catch can) vents. It permits venting but prevents oil from escaping the engine if the vehicle is accidentally inverted.
SPECIFICATIONS
Threads: 7/8-14 UNF (10AN ORB)
Barb (OD): 0.75" (19mm)
Material (valve): Stainless Steel
Material (retaining ring): Stainless Steel
Material (o-ring): FKM
Material (body): 6061 Auminum
Surface (body): Type-II Anodized