Copper Pipe Types Explained: K vs. L vs. M
Copper Pipe Types Explained: K vs. L vs. M
We referenced Type M copper in our piece on pinhole leaks, but the full picture includes three standard designations, each with a different wall thickness. Here’s what the letters actually mean.
Type K: Thickest Wall
The heaviest-duty of the three, Type K is most commonly used for underground service lines where extra durability matters, and in some commercial applications. It’s overkill for most interior residential supply lines but shows up where the pipe needs to withstand more.
Type L: The Common Middle Ground
Type L is a common choice for residential water supply lines, balancing durability against cost and workability. A lot of quality residential installations from the postwar era through more recent decades use Type L.
Type M: Thinnest Wall
The thinnest and least expensive option, Type M was widely used in residential construction, including much of Torrance’s postwar building boom. Its thinner wall gives it less material to absorb internal pitting corrosion before a leak develops through the pipe wall – which is exactly why it shows up disproportionately often in our pinhole leak calls.
How to Tell What’s in Your Walls
The type is typically stamped directly on the pipe itself, visible at any exposed section – under a sink, at a water heater connection, or during a repair. If you can’t find a stamp, a licensed plumber can generally identify the type from wall thickness and other characteristics.
