Flow Charts for Pipes

Q. "How do I determine what type of tubing I have?"
A. In copper pipe, Type L (which in most cases is stamped or printed with blue writing) and Type K (which in most cases is stamped or printed with green writing) are typically used for residential plumbing and is sold in nominal sizes which are approximately an 1/8 inch less than the actual outside diameter. Type K has the heaviest wall thickness, and is typically used for burial underground. Type L is more of a multi-purpose tubing, and is used for most other installations. Type M, which in most cases is stamped or printed with red writing, has the lightest walls (meaning it has the largest inner diameter of the three types listed) and is typically used for drainage and other low-pressure applications. Please keep in mind that wall thickness will vary with nominal sizes, and the resulting inside diameter is always within a few hundredths of an inch of the nominal size. In PVC pipe, Schedule 80 has thicker walls than the standard Schedule 40, and as a result, a smaller inner diameter. However, this is only true of Schedule 80 pipe; the fittings are different in that the outside diameter of the fitting gets larger, so it can accomodate the pipe. In older designation systems, Schedule 40 was designated as Standard Wall pipe, and Schedule 80 was designated as Extra Strong walled pipe. Schedule 40 is the most widely used form of PVC pipe.