The size of a natural gas orifice typically varies from about 0.014 to 0.026 (inch diameter). It totally depends on the unit's gas pressure. For deep information 0.026′′ (1,835 Btu/h at 4′′ pressure) for commercial cooking units and 0.018′′ (879 Btu/h at 4′′ pressure) for a natural gas water heater pilot.