Hook number ranges could be confuse, specially if you are trying to follow a pattern from a different country.
We could find two different hook categories: steel hooks (for lace) and normal hooks. In the left column we have steel hooks with their own nomenclature and its equivalences in the metric system (millimeters) for USA (column 2), English (column 3) and the popular Clover brand (column 4).
In the metric system, millimeters are referring to hook´s edge diameter. Because of this is something quite difficult to measure, hooks are usually coming with the name engraved, to avoid that after some time with the usage the print would be damaged and number reference may be lost.
In the right column, you could find as well the different names of most popular hooks. Again, we compare metric system hooks with USA, UK and Clover brand.
It is possible that some hook manufacturers may have other different classifications for specific hooks but, in general, every thing we have include at this compilation chart is the most usual and /or popular.