A fitting that forms an angle of less than 180 degrees (3.142 radians) from the straight flow. one connecting end has standard pipe threads, or is unthreaded and designed to accommodate a pipe. the other end has machine threads (straight threads other than pipe or hose series) designed to accommodate a tube, or is unthreaded and designed to accommodate a tube. it may have side or heel inlet(s). see also elbow, pipe; elbow, tube; and connector, multiple, fluid pressure line.