Now that is interesting.
13 for Dayco is 13/32 (nominal top)
Gate's listing by application starts with a 7. I haven't checked into what that represents.
Maybe tommorrow I'll have a chance to dig into the industry sizings vs design.
If someone has any old Chrysler belts it would be great to get some measurements.
Or some belt catalogs from the late 60s and 70s that would be interesting too.