Fluval Universal Venturi Valve for Power Heads and Filters Adjustable dog harness with adjustment sliders and quick release snaps Fits BioLife 35/55 power filter and Fluval U line of underwater filter models U1, U2, U3, U4 It is also used for AquaClear power heads Comes in polybag with header Measures 1/2-inch length by 1-1/5-inch width by 2-1/2-inch height