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Why is type M- L- K pipe called this?

grindog Member Posts: 121
they have different hardnesses. Mis softest and k is hardest. In massachusetts we use L for all water piping in the building and type K for the water service coming in from the street. M is used for heating unless otherwise specified.


  • John@Reliable_5
    John@Reliable_5 Member Posts: 76
    Copper pipe markings

    Anyone know why copper pipe is rated like this. Is it because of drill size (thickness) or some other reason.I hate it when someone asks me a question I can't answer. John
  • brucewo1b
    brucewo1b Member Posts: 638

    Type M is thin-walled, system pressure as in water boiler runs to baseboard. Type L is medium-walled usually used for street pressse ie hot and cold water pressure and Type K is thick-walled
  • Mike T., Swampeast MO
    Mike T., Swampeast MO Member Posts: 6,928

    According to www.copper.org the K-L-M designation refers to wall thickness:

    "Types K (heaviest), L (standard), and M (lightest) wall thickness schedules as classified by ASTM B88"

    Am still searching for the origin of those designations. I've found that the origins of nomenclature are EXTREMELY difficult to find on the web and almost never mentioned in printed trade references. You have to find the "weird facts" sort of sources...
  • Mike T., Swampeast MO
    Mike T., Swampeast MO Member Posts: 6,928

    It doesn't help that even when quoted "K-L-M" Google returns hits for "KLM". KLM is both an airline and a major mining company...

    "M-L-K" gets almost nothing besides typos for "milk"
  • bob_50
    bob_50 Member Posts: 306
    Copper Tube

    is availabel (ASTM B 88) in K,L,M,DWV,Medical Gas,ACR and G. Wall thickness varies from .025"-3/8"M to .405"-12"K. There are other types available from the mill on special order. The letter designation has nothing to do with hardness. I have no idea where the designations came from. The first documented use of copper tube to convey water was 5,000 years ago. It was used to supply water to Pharaoh Cheops bath. It is still in usable condition. I wonder what 5,000 year old PEX will look like. bob
  • brucewo1b
    brucewo1b Member Posts: 638

    If your pulling them out of a concrete slab I'll wager that the PEX wins
This discussion has been closed.