I am trying to install a new vanity and the age of my house is killing me. The pipe coming out of the floor is 1-3/8 inch pipe. I have a new sink drain that is 1-1/4 inch so I have a trap adapter for that. Problem now is that I have to connect it to the other pipe. The only adapters I have found are for 1-1/4 inch.

I don't even know is such an adapter exists. I can't seem to find anything online that is what I am looking for. What can I do to connect 1-1/2 inch abs to my 1-3/8 inch pipe?

I have seen several cases of "There is no such thing as 1-3/8 inch pipe." If it helps, my house was built in the 50's and the pipe is labelled "galt brass". I live in Southeastern Ontario Canada if that helps at all. I will post a picture, with tape, once I am near a computer.

  • 1
    Where are you getting this 1-3/8 pipe size? Pipe sizes are "in nane only" and actual measurements are different. Commented Jan 16, 2017 at 0:39
  • I was measuring the diameter of the pipe. I had to call it something.
    – Matt
    Commented Jan 16, 2017 at 0:51
  • Pipe is described by its inside diameter. You may have a thin-wall variety, or something else.
    – isherwood
    Commented Jan 16, 2017 at 1:01
  • The wall of the pipe was definitely thin. Just under 1/8th of an inch. My measurement was the outside diameter. While I am certainly wrong with what I am calling it it did not fit the standard 1 1/4 inch parts I was finding. Was not sure what else to call it.
    – Matt
    Commented Jan 16, 2017 at 1:06
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    Matt I respect being new to this stuff. Learning time: pipe is always described in a seemingly-arbitrary trade size, differing by about 3/8". What @isherwood is saying has historical basis but is misleading, because every threaded pipe in a given trade-size has the same outside diameter. That rule only breaks down for pipe not intended to be threaded, e.g. copper water pipe, which uses the same concept, but its trade sizes are only 1/8" smaller than actual. Commented Jan 16, 2017 at 2:03

5 Answers 5


Your pipe is 1" trade size.

It's very standard and you'll have no trouble finding parts.

The "trade size" is a weird thing that happens with pipe. Actual size is somewhat larger than trade size. (a rule of thumb is an extra 3/8", that works for common household sizes up to 2-1/2").


Different materials and grades of pipes need different wall thicknesses to do the job. However, pipe threads are always cut to the outside diameter of the pipe. Needing to have a huge variety of slightly different pipe elbows and fittings would be completely crazy, and invite accident. So they standardized outside-diameter. Inside diameter varies with material and grade. Result: a 1" fitting will fit anything from Schedule 10 to the reactor grade stuff.

All 1" trade size pipes have an OD of 1.315". Because of that, I'm entirely confident that your pipe is 1" trade size, regardless of some interesting questions about the material. If you had asked ID, that would be a different kettle of fish...

The 1.315" size is based on the metallurgy of early pipe; in that day, the inside diameter actually was 1".


At the guidance of a employee at a local hardware store I tried a 1 1/2 ABS to 1 1/4 Copper adapter.

1 1/2 ABS to 1 1/4 Copper adapter

The dimensions of that adapter were different then just a regular 1 1/4 to 1 1/2 adapter (which I previously tried). So even though the pipe was measured at 1 3/8, the copper adapter fit near perfectly. Better when tightened of course. After running water though it no leaks were observed.

  • The size matchup makes sense since copper actual is 1/8” larger than its trade size. If it leaks, try something intended for 1” threaded pipe. (Pipe is referred to universally by trade size.) Commented Jan 16, 2017 at 2:37
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    Matt, please accept your answer to resolve this question.
    – isherwood
    Commented Feb 16, 2021 at 16:39

Check hardware stores for an adapter. You might be able to use a rubber type that you can cinch down via the hose clamps.

  • Thanks for the delete, Naill C. So this means that you guys really don't want an answer to Matt's inquiry. You all are talking about "trade sizes" and threaded pipe sizes etc. which does not answer his inquiry. You need to know what kind of pipe material he is working with. He most likely has 1-1/4 heavy wall brass drain tubing coated in nickel or chromium which is hard to come by today and was used years ago.
    – d.george
    Commented Jan 16, 2017 at 12:19

Look up the Proflex 3001-150 Shielded Pipe Coupling. This coupling was made for this specific purpose.

Some older homes (including in the 1970's) used 1 1/2" copper drains which actually measure out at 1 3/8" diameter, which is what you have.


I had the same problem with my clawfoot tub years ago. A local plumbing supply house suggested I wrap kite string around the 1 3/8 inch pipe until it fits snugly with the 1 1/2 pipe and then tighten the nut. It hasn't leaked in 35 years.

If I ever have to do this again I would coat the whole thing with pipe dope just to make sure. By the way, there is such a thing as 1 3/8 pipe. Look for clawfoot tub drain parts. I just found a slip joint nut an o-ring that goes from 1 1/2 to 1 3/8 here https://www.plumbingsupply.com/clawfoot2.html

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