I am fairly sure type M is used in normal residential construction. L is heavier and use for more underground or commercial applications. You can quickly tell t

I am fairly sure type M is used in normal residential construction. L is heavier and use for more underground or commercial applications. You can quickly tell the difference because M has red writing on it, while L have blue. The problem is there are no "L" fittings and the normal fittings used for L copper can be quite poor. For this reason and others, some people like ProPress fittings which are very high quality (and expensive).