Threaded couplings for suction or discharge of water or other fluids. Standard threading is NPSM; National Pipe Straight Mechanical. 1-1/2" and 2-1/2" are available with additional NST thread; American National Fire Hose Straight Thread. (NST does not interchange). Pin lugs are on all sizes of female end. 2-1/2" through 6" also have pin lugs on male end.