Why Don’t My Fittings Fit?

Copper 90 Degree Elbow FittingYou’ve probably noticed that not all fittings and pipe are the same. In fact, you might have noticed that it’s almost easier to consider the pipe size to be a name rather than a description, since your measuring tape doesn’t seem to help you much. Really, is it too much to ask that a 1/2″ fitting actually measures 1/2″ somewhere?

Apparently so, but why?…

(This article has found a new home on our site!)

To learn more about the history of fitting sizing and how to determine what size you actually have and/or need, just click here.

5 thoughts on “Why Don’t My Fittings Fit?

  1. Jon Dowie

    So I thought I had 1/2″ copper pipe for my water in my 1950’s built home. I bought 1/2″ fittings and the pipe seems a hair too big for them. None of the fittings will go on at all. Do I actually have 5/8″ copper pipe, or do I need a different type of fitting. Also, I am trying to go from 3/4″ pex to this mystery copper. HELP!?!?!?

    1. PlumbingSupply.com Post author

      Hi Jon,

      If your copper pipe measures 5/8″ outside diameter then 1/2″ sweat fittings will solder onto it. 5/8″ outside diameter copper pipe is 1/2″ on the inside and is how sweat fittings are referred to in size.

      In the plumbing industry, sweat copper fittings are sized and named according to the inside diameter of the copper pipe they will attach to. The common copper plumbing pipe sizes are 1/2″, 3/4, 1″, 1-1/4″, 1-1/2″ and 2″ and are all referencing the inside diameter. Each one of these sizes is available in different thicknesses. Type M has the thinnest wall and is the minimum thickness that can be used for potable water applications. There is also Type L and Type K. Type L is thicker than Type M and Type K is the thicker than Type L. Type L is very rarely used for common residential applications mostly due to the cost of this thicker pipe.

      Since copper pipes are made in different thicknesses the outside diameter is made constant and the inside diameter will vary slightly depending on the thickness of the pipe. This slight difference in the actual size of the copper pipe is referred to as nominal (existing in name only), meaning there is some give or take in the actual inside sizing reference.

      If your 1/2″ N (nominal) piping is slightly larger in diameter and your fittings will not go on to it, then it is possible your pipe could have been slightly frozen at one time and the pipe was expanded. You were lucky the pipe did not burst, but once copper pipe is expanded it does not revert back to its original size.

      If this is the case and your pipe was frozen enough to expand the pipe, then you will need to go back further down the line and get to a place the pipe was not expanded to sweat your fittings onto it and replace the pipe that was expanded. You may also need to do this when making your PEX to copper connections if the fittings aren’t fitting correctly.

      We hope this has helped you, but if you need further assistance, please feel free to contact us at sales@plumbingsupply.com. Thanks for reading!

  2. l. beckner

    i work at a housing complex of over 400 units. the place was built in the 50’s. , for a local industrial complex of military nature. on many occasions we have the problem 0f the old 3/4 copper pipes being to big for the sweat fittings sold today. been told the frozen pipe story which sounds highly questionable, also heard this idea that it’s to big cause it was “military copper”. would just like an answer that makes sense.. L B

    1. PlumbingSupply.com Post author

      Hi LB,

      While we have never heard of “military” copper, it is possible that a different type of copper piping was mistakenly used – namely ACR copper designed for use in air conditioning or refrigeration applications which is sized differently from copper pipe designed for use in plumbing systems. However, it is far more likely that you have indeed had frozen pipe problems. When you think about it, it’s not so questionable as it might seem at first. Pipes that haven’t been purposely drained always have a little bit of water in them. Frozen water expands. Anything that is holding that water when it freezes will either also expand or burst. Since copper is a more malleable metal than say galvanized steel, it will expand as far as it can before it breaks. If there’s not a lot of water in there, the freezing process could cause expansion without breaking the pipe. Once the temperatures warm up again it can contract again slightly, but there’s no way to make it contract all the way back to its original size. Numerous small expansions over time (i.e., the last 60 years or so!) would definitely change the size of your pipe.

      Copper pipe has amazing durability and many excellent qualities that make it ideal for plumbing, but keep in mind that sometimes copper pipe will last you 100 years and sometimes due to things like thermal expansion and water quality, you’re looking at 25 years. When making repairs, we suggest trying to move a little further down the line to see if you can find an insulated or unexposed area where expansion may not have occurred, or possibly purchasing slightly larger fittings (although you may not be able to make those work either). For more advice on how to handle your unique situation, we recommend talking with the plumbing pros at http://plbg.com – they love a good plumbing challenge!


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