Abstract: A hollow, cylindrical water hammer arrestor includes an axial passage; two externally threaded extensions disposed at both ends respectively, each of the externally threaded extensions having a diameter less than that of the axial passage; a plurality of first rings disposed in the axial passage, each of the first rings having a plurality of teeth formed on an inner surface; and a plurality of second rings disposed in the axial passage, each of the second rings having a smooth inner surface. The first and second rings are alternately disposed from one end of the axial passage to the other end in the axial passage.