Just in case you haven’t found it yet, for a Zenith with a 24T2 fitted with a number 14 choke tube the correct size for the air jet which fits in the hole you’re pointing to is 1.50, with the slow running tube (or jet) next to it being 50.
Don’t forget that you can fine tune the tick over with the Air Regulating Screw on the side of the venturi in the top cover of the carburettor. Remember that it adjusts the air part of the mixture, not the fuel, so screwing it out makes the tick-over mixture leaner (less fuel) and screwing it in makes it richer (i.e. more fuel).
Best of luck with it.