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The Difference Between Type M, L And K Copper Pipe

Over time, great durability and low maintenance have been proven in regards to using copper pipe and fittings. They outlast almost all other material, are resistant to bacteria and corrosion and are very easy to work with as copper pipe bends fairly easy, decreasing the requirement of cutting, connections and fittings. With a few options available, knowing the difference is necessary to achieve a successful application. Other than a few notable markings (described below), it may be a bit difficult to tell the difference between type M, L and K copper pipe by simply looking at the outside. All three types have the exact same OD (outside diameter) measurement thus making the fittings universal, however, the ID (inside diameter) measurement is where the sizes vary due to the wall thickness and pressure tolerance.

*Common sizes range between ½” and 2” copper pipe


Thin Wall

Often used in residential, interior applications such as water heater systems and non-potable water distribution

Should not be used in plumbing applications

Sold In rigid lengths only

Lower pressure tolerance

Distinguished by red lettering on the exterior of the pipe


Medium Wall

Often used in exterior applications, hot water distribution, water distribution above and below ground, commercial plumbing and gas lines

More expensive

Sold in hard, straight lengths and in soft coils

Distinguished by blue lettering on the exterior of the pipe


Thick Wall

Often used for gas lines, fuel lines and fire protection systems

Sold in hard, straight lengths and in soft coils

Higher Pressure tolerance

Distinguished by green lettering on the exterior of the pipe

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