Looking for the two knobs that operate the sliding air vents below the glass doors. It is a push-on knob with no set screw; looks like black Bakelite or similar. They are an 1 3/4" on the top face and 7/8" on the base face; the top diameter is 1 3/8" and the bore is 3/8". About 1 1/4 deep. Any help directing me to purchase these would be very appreciated! We purchased our GB stove about 1983.