This page on Amazon has the diameters:
https://www.amazon.com/gp/product/B00X2YA830/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&th=1
Although it only goes down to #7 which it lists as: SIZE: 0.98" (25 mm) height x 0.75" (19 mm) diameter
This page:
Has the other sizes but without measurements
The Ner Mitzvah catalog also has sizes listed:
https://www.nermitzvah.com/catalog/product/view/id/3489/s/7-oil-glass/category/71/
If it is 1/2" then that would be around 12.7 mm so that's probably a 5 or 6 (I'm guessing here)