Maintenance NOx(A) – exchange Sintered filters and O-rings Procedure NOx A3 - Replacing the critical orifices, o-rings & capillaries Parts you need: Critical orifice 4mil [800-360001], Critical orifice 10mil [800-360002] Tools you need: 7/16″, 1/2″, and 9/16″ wrenches, tweezers