Shouldn't 'double zero' be 'double zeros'? For example, we say 'double doors,' not 'double door.'
It isn't common to follow 'double' with a plural, especially not with numbers.
However, the reason we say "double doors" is that, in this context, "double" is the name for the style of doors. You could have two doors that lead into the same room but you wouldn't say the room had 'double doors' unless the two doors were together. If a room had two separate doors you would just it had "two doors". "Double doors" is a compound noun that describes a set of doors styled that way. Likely there are other similar examples too.