A hex nipple is a fitting used to connect two pipes or hoses. It is a type of reducer, and is composed of a short piece of pipe usually provided with male threads at each end for connecting two other fittings. Hex nipples are commonly used to connect hoses to valves, tubing, or pipes. They are available in a variety of materials, including MS, and stainless steel. The most common size is 1.5 inch.