Have read some piping isometrics that state "3000# FS" fittings. I know it is referring to Class 3000 pressure rated fittings, but what exactly does the "FS" stand for?
The supplier we use gives us 2M threaded fittings made from the same 'body size' as the 3M socket-welded fittings; 3M threaded stuff is made similar to the 6M socketwelded stuff. When purchasing, do not buy 3M threaded expecting to get something similar to 3M s.w. you bought last month. 3M threaded looks like small-craft boat anchors.