Some jets are a percentage of flow and some are in mm dia.
We just pulled the Main Jet from Our China Doll and it was 70mm (It was actually a very loose 65 but not quite a #70)They sell jet drills but they are very expensive and not the same as the number drills you might buy. The best is to purchase jet reamers. The are tapered reamers that are easy to use and get accurate hole size. There not cheap but cost about 1/2 as much as the jet drills.
Be sure you know how to reed the plug before you start jetting.
The slide cut away, the needle jet and needle position and the main jet can all be changed and all effect different throttle positions. Carb Jet Reamers
Carb Jet Reamers