The overflow box effectively transports aquarium water to under cabinet sumps, refugiums, or wet/dry filters. High quality overflow boxes feature bulkhead fittings for secure and convenient installation. U-tube style compact overflow boxes are designed to fit between your tank and your wall to maximize space usage in your aquarium setup. With only 3 in. required between your tank and your wall, these boxes are excellent for optimizing space. Each box includes everything required to attach it to your system. Includes: U-tube, cylinder (round) foam, nylon screw and wing nuts, and pre-filter box. PF-Nano has 3/4in bulkhead, PF-300 - PF-1200 have 1in bulkheads.