I just bought this adapter and for some reason, it won't fit with 3/8 or 1/2. enter image description here enter image description here

Any recommendations that would fix the issue? I am not sure what my water line size and from what I know, 3/8 and 1/2 are standards. Is there any specific parts that I'm missing?

My current shutoff valve: enter image description here

My current supply hose: enter image description here

  • I'm trying to connect additional water outlet for my RODI. I bought this product: ibb.co/bW0Nw4h this product has 1/2 and 3/8 thread that won't even fit in my water line
    – jerz
    Commented Apr 27, 2023 at 4:30
  • Here is the product link: amzn.to/3L8CIoh with specifications.
    – jerz
    Commented Apr 27, 2023 at 4:31
  • I am trying to connect my RO/DI water filter system. my RODI uses 1/4 tubing which is no problem. the Issue im having is that the product i bought amzn.to/3LelR3t with 3/8 and 1/2 thread won't even fit in my under sink water line. Not sure what standard size is my under sink water line thread.
    – jerz
    Commented Apr 27, 2023 at 5:09
  • Photo of that fitting, and knowing which country you are in, might be helpful. In the US, I think the flexible tubing that runs from the cut-off valve to the sink is usually a 3/8" Compression fitting at the cut-off valve and 1/2" Iron Pipe (FIP / IPS) connection at the faucet. What you need, if attaching this to one end or the other if that hide, is fittings on both sides that match one or the other if those sizes, unless you want to replace other parts too
    – keshlam
    Commented Apr 27, 2023 at 6:52
  • 2
    Put your photos and all other information in your question, please, not down here. See How to Ask and take the tour.
    – isherwood
    Commented Apr 27, 2023 at 13:54

1 Answer 1


To put it where you want it, it has to be the same size and thread on both sides, since you're inserting it into an existing connection.

From the diagram, if you bought the right size unit, they expect you to use the adapter ring to fit one side it the other, depending on whether your existing fitting is 1/2" or 3/8". The adapter should either screw into the hose or onto the valve.

If it doesn't fit either way I'd say you have the wrong version of this add-on valve and need to figure out what size you pipe fittings actually are are. Something metric?

  • it won't fit using 3/8..might be 1/2
    – jerz
    Commented Apr 28, 2023 at 8:27
  • i measured the thread in the pipe and its 0.67 inches. not sure if that is the standard
    – jerz
    Commented May 2, 2023 at 1:54

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.