Annual service parts kit for the venerable Scubapro MK-15 first stage regulator (Scubapro part # 10.600.041). This includes the seat, o-rings etc, everything that wears out and needs to be replaced to prevent leaking and poor performing scuba regulators. These parts, combined with cleaning and tuning will bring your reg back up to factory specs. Of course, since this is life support equipment, installation should really be done by a trained tech and should not be undertaken lightly by a novice.