Abstract: A high pressure rotary gas meter is described herein with an exchangeable cartridge which has a meter body surrounded by an open bracket. The meter body can have a chamber in fluid communication with an inlet and an outlet. An impeller can be located in the chamber and can include a plurality of rotors connected to a gear box and a meter index to display flow information. A counter can be coupled to the meter index, for counting revolutions of the rotors and for translating the revolutions into a measurement of fluid volume. A removable first sleeve insert and second sleeve insert can permit fluid to flow into the inlet port and out of the outlet port while simultaneously securing the bracket to the meter body.