The garden hose water valve on the exterior of the house has started dripping, so I attempted to replace it. I went to the hardware store and they had plenty that were 1/2" NPT and 3/4" NPT (the part that attaches to the water supply pipes, not the hose adapter itself). I got one of each just incase my memory was bad.

I managed to get the old one off of the threaded nipple pipe, but noticed there was a small chunk missing on the very edge of the nipple pipe, so a small gap in the threads. However, further down the pipe it had complete threads, so I thought "good enough for now" and tried to screw the new valve on.

The 3/4" was clearly too large, so I tried the 1/2". I struggled for a good 15 minutes, it was just not fitting. It kept trying to screw on sideways (I guess because of the missing chunk?).

Eventually I decided to try to put the old one back on, and it fit perfectly, no problems! I was surprised.

I'm trying to figure out what is going on. Did older houses (1950's) use a thread size somewhere between 3/4" and 1/2"? Did the old pipe and valve corrode together evenly over time, and thus they are a new strange thread that fit together? Or was that missing chunk really the issue (no explanation on how I managed to put the old one back on so easily).

  • there is also 5/8 type which is in between 1/2 and 3/4
    – Traveler
    Aug 26, 2023 at 23:03
  • I don't usually suggest this, but maybe it's time to try to repair the existing... Aug 27, 2023 at 0:02

2 Answers 2


Depending on where you live it used to be very common to use an "Arrowhead" sillcock. This uses a different proprietary threading than 3/4" hoses but they can look similar.

Arrowhead brass has some tell-tale insignia you can look for.

A photo of the part you removed and the sillcock might help!


The simple solution is to take the now removed sillcock to the store and try it on the various and sundry fittings until you find one that it threads onto. Now you know the size & type of threads that you have on the pipe coming out of the wall.

You now have two options:

  1. Pick up a new sillcock that matches this thread
  2. Pick up an adapter to screw onto the pipe from the wall that then provides threads that match the sillcock of your choice.

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