I think the classes have remained unchanged from the opriginal SAE classification. This chart goes into some detail about taps.
http://www.newmantools.com/taps/tapclass.htm
This stuff hasn't changed much over the years but only a few industries worry about bolt hole and nut fit to a fastener. Aviation still uses them for the older equipment like the Radial engine cases where a lot of studs are used in aluminum castings. My Rex suply catalog has taps in every fit but they have pages & pages of taps to poor over till you find what you want. Most machine shop suppliers have these types of products.