Lifegard Aquatics Double Threaded Bulkheads are constructed of the highest impact-resistant PVC. It eliminates the possibility of finding hidden cracks when filling the aquarium. Threaded on the inside and outside and are all FPT BulkheadBulkhead has inner threaded fittings on both endsJet black color to blend in with the back wall of the aquariumBulkhead fittings are used for attaching filters, pumps, protein skimmers and other devices to either an acrylic aquarium or reservoir using standard PVC fittings. To install, drill the appropriate size hole where you want the bulkhead located and install the bulkhead with the gasket between the tank and the bulkhead flange. Hand-tighten only, then one quarter turn to seal. Specifications:1" FPT: Requires 1-3/4" Diameter Hole