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7 In this close-up, we see the actual piston and slots that allow the fluid to flow from one side to the other as the shock shaft moves in and out. Small drilled holes, called bleed holes, in the piston allow slow speed movement and the size of those holes regulates the amount of resistance. As the shaft speed increases, the pressure becomes too great for the small bleed holes to flow enough fluid past the piston. The steel discs attached to the sides of the piston deflect and allow a greater volume of fluid to pass through the piston. The size, number of, and thickness of, those discs determine how much pressure is needed to open them and the amount of volume of fluid that they will allow to pass through.