These weirs feature a polycarbonate faceplate attached to the mounting ring with a neoprene gasket that seals against leakage. They are intended for measuring non-point storm-water runoff, low-flow in sewer pipes, free flow from open-end pipes, and for collection-system acceptance testing in either gallons per day or cubic meters per hour. Models are available for pipe sizes 6 through 16 in., with adapters for pipe sizes of 18- to 48-in. diameter. A thumb-wheel at the top of the mounting ring allows the weir to be positioned in the pipe without tools.