A pipe Nipple is a short length of pipe with threaded ends, used to connect two other fittings or pipes. It is commonly used in plumbing, heating, ventilation, and air conditioning (HVAC) systems where pipes need to be joined together, and the length and diameter of the connecting pipe are crucial. Pipe Nipples come in different lengths, diameters, and materials, including black steel, stainless steel, brass, and copper, among others. They may have one or both ends threaded, depending on their application and usage.