Hello, I've been trying to learn exactly how materials are specified, with particular reference to pipes and fittings, and I've come across some conflicting information and apparent confusion. The callouts I've been coming across have an ASTM #, grade #, amd sometimes a UNS#. For example: ASTM A403 Grade WP316 (UNS S31600) I'm fairly certain the ASTM number specifies the actual material composition and the minimum alowable mechanical properties, like tensile strength and yield strength. Does the ASTM number actually mean anything itself? i.e. does the 'A' or the fact its in the 400s indicate anything in particular about the material. From what I can tell, the grade has more to do with the finish or how it is manufactured. I found that WP indicates wrought in this case. Again, does the number itself mean anything? I have the most confusion with the UNS number. I can't tell if its just a different was to specify the same thing or if it adds more description to what has already been listed. Any light you can shed on this subject would be most appreciated, thanks in advance for your help.