^ true. Pipe is a nominal measurement. The id changes per the schedule (wall thickness) and the od stays the same so the same fittings can be used.
6 inch pipe measures around 6 3/4 o.d. sch 10 has a thinner wall than sch 40 therefore had a larger id.
tubing can go either way- take copper for example. 2 inch copper tubing is actually 2 1/8 od and 2 id. You have to specify "od" on tubing to get an od measurement.