The flow of liquids in pipelines plays an important role in industry and commerce. Under most circumstances it is essential to know whether or not there is a flow in a pipeline, and to act upon that knowledge. That is the reason for, and the function of, McDonnell & Miller Flow Switches. Includes 4 stainless steel Paddles: 1", 2", 3", 6". NEMA Enclosure Type 4X. Watertight, dust tight and corrosion resistant.