Martin 5J 1/2 Quadraflex Coupling Flange, Sintered Steel, Inch, 0.5" Bore A, 0.5" Bore B, 3.25" OD, 2.875" Length, 0.125" x 0.063" Keyway For use with some flexible coupling assemblies (sold separately) in the Martin Quadra-Flex series Steel sintered with powdered metals for strength, durability, and corrosion resistance Transfers shock and misalignment to the center element of the coupling assembly for reduced wear on the shaft assembly Teeth help to distribute torsional load across the flange and sleeve, reducing wear and extending service life