When it comes to working with copper pipe there are a few choices that you will need to make when you got to purchase the copper from the plumbing supply store. If you have not read the intro to copper pipe yet, that would be a good place to start as this plumbing lesson will go deeper into the different grades of copper plumbing pipe. But just as a recap of the first lesson, The difference in the letters ( I.E. M . L , K ) is actually the level of thickness of the wall of the copper. Lets start with the different grades of pipe.