that's the $64,000.00 question....
off the top of my head:
I have Indestro 15° offset double-end box wrenches
I have Indestro 45° offset double-end box wrenches
I have Elora 60° offset double-end box wrenches
I'd have to go dig out catalogs, but I believe Thorsen used an odd number on some of their double-end offset wrenches which was not 15°, 45°, or 60°. (I could be completely off the mark there.)
I'm sure others will chime in here.