Would Like to replace the supply line to the toilet.

However I noticed that the side connected to the water valve measures about an inch wide, and I don’t see that as a standard size at the major hardware stores.

Is this a standard size that measures about the diameter of a us quarter?

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  • 1
    I think you need a female-to-male adaptor and reducer if the thread is outside of the existing fitting. Otherwise use a male-to-male reducer to reduce to the correct size (3/8").
    – r13
    Jan 18, 2022 at 1:06

1 Answer 1


That's 1/2 FIP, and someone put a sink valve on there for some reason.

This should work: https://www.homedepot.com/p/BrassCraft-1-2-in-FIP-x-7-8-in-Ballcock-Nut-x-16-in-Braided-Polymer-Toilet-Connector-B8-16DL-F/206121724 - search for "1/2 FIP ballcock"

Or you can search for 1/2 FIP to 3/8 female to male reducer such as https://www.homedepot.com/p/BrassCraft-3-8-in-FIP-and-1-2-in-FIP-Brass-Water-Supply-Adapter-BCRP16-D/206069675

  • Thanks that is helpful. For understanding, why does it measure a full inch but is called 1/2?
    – P.S.
    Jan 18, 2022 at 1:38
  • 1
    Think pipe size, not thread size. Pipe uses internal diameter, so add wall thickness and thread thickness.
    – isherwood
    Jan 18, 2022 at 17:43
  • 1
    @P.S. The inner diameter (id) of the original pipe was indeed 1/2 inch, and they standardized the outer diameter (od) to 0.840 inch based on the wall thickness they needed for the strength. But manufacturing got better, and the pipes got thinner, so the id got larger, but they kept the od the same, so pipe could still connect. And now you have today's situation where the number seems to have no connection with the size.
    – Ariel
    Jan 18, 2022 at 22:19

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