A fitting is for use in a fuel gas system having an access port for providing access to the system. The fitting includes a fitting body and a valve core. The fitting body includes: a first end for providing mating connection of the fitting body to the access port, a second end for providing connection of an accessory, and a central bore of at least 13/64″ through the fitting providing an opening through the fitting body between the first end and the second end. The valve core is removably received in a valve receiving means of the fitting body, and includes a valve operator actuatable to open a fluid connection between the first end and the second end. The valve core is removable from the fitting body so that an unobstructed volume of the central bore can be available for a flow of fuel gas into the system.