Suction Hose Coupling: Threaded couplings for suction or discharge of water or other fluids. Standard threading is NPSH, National pipe Straight Hose 1-1/2" and 2-1/2" are available with additional NST thread;AmericanNational Fire Hose Straight Thread (NST does notinterchange) pin lugs are on all sizes of female end 2-1/2" through 6"have pin lugs on male end.