Is it possible to put a #0 barrel on a #1 frame? I take it that the frame size is the frame where the action and stock is correct? Why then do they stamp the frame size on the barrels?

Please excuse me I'm a greenhorn here. Can you have a #1 frame with #0 stamped on the barrels? The more I get into this the more I get confused and have becoup questions.
Thanks, you guys are great.
Steve B.