I've learned that a 1-1/2 inch ABS pipe isn't really 1-1/2, but a 2
inch copper pipe is actually 2 inches. Will such an adapter fit both?
Is there such a thing as a "specialty" adapter for ABS to copper pipe,
since they seem to use different rulers for measurement?


First off, showers are 2", not 1 1/2". Bathtubs are 1 1/2". Yes, there are
adapters made to join pretty much anything that should be joined. You can try
Home Depot, ask a clerk for their 'Fernco' fittings, Fernco is one of the
largest makers of rubber couplings. Each fitting will have a label which will
list the types of piping that will fit. If they don't have what you want, try a
real plumbing supply.

--
Dennis