I got ya now. "ASTM D-1785" is the key. Nice if it also has a pressure rating (easier to understand and remember). My point was just that the presence of "Schedule 40" is irrelevant, except that the pipes and fitting will physically fit together. I checked the four sizes of pipe in my garage and they all have pressure ratings and ASTM D-1785. My one piece of evil 4" DWV has a different ASTM number.
To put it another way, we should all quite calling it schedule 40 and use ASTM D-1785 instead?