AIRTY 2 Bulkhead Fitting (Slip x Slip) The composition of our Bulkhead Fittings is black ABS plastic. This provides a level of strength and longevity out of reach of other Bulkhead Fittings. Gaskets are made of Thermo Plastic Elastomer (TPE) for extra strenth and durable. Slip x Slip To determine which side of the Bulkhead Fitting is Slip or Thread when placing your order please keep in mind that the side with the flange is listed first while the shaft side is listed second. Therefore, our Bulkhead Fitting, Slip x Thread would have the slip on the flange side and the thread on the shaft side. Great for Water Tanks, Aquariums & Ponds. Easily insert pipe into or through tank walls, fountains, or other projects