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I am having trouble fitting a vacuum breaker (or even a hose) with 3/4in FHT into my hose bib. The threading seems compatible, but I am not able to screw them all the way in- and the connection leaks. Another bib in my house has a Watts NF8 vacuum breaker attached to it which works perfectly, hence I assumed both bibs have a standard MHT. Any ideas what might be wrong? Is there any chance the bib has an MPT connection on the hose side?

I did read about some hose bibs having fine threading and requiring an adapter. But threads on these don't look like they are fine.

Hosebib

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    Hard to tell from here, but it looks like the threads at the leading (output) edge of the bibb are smaller diameter. Either they're damaged or there's some sort of (very odd, I know) insert into the bibb outlet that's causing you consternation. With the trouble you're having, it might be better to replace the whole bibb.
    – FreeMan
    Commented Jun 14 at 12:19
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    Those threads look damaged - as if in the past someone cross-threaded something on there and continued forcing it.
    – Solar Mike
    Commented Jun 14 at 12:20
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    As a quick fix, you might be able to stack rubber washers or O-rings in an adapter to make it seal even though it doesn't thread all the way.
    – jpa
    Commented Jun 15 at 6:41
  • Thanks everyone for their replies.
    – user192856
    Commented Jun 16 at 14:08
  • There could have been a device attached to that bib (such as a backflow preventer) that had a lock screw installed. If someone forcefully removed that device without first removing the lock screw, the threads would get damaged exactly like that. Commented Jun 17 at 6:06

4 Answers 4

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I agree that the threads look a bit rough. Rather than replacing the faucet, should that be challenging, consider chasing or repairing the threads. You can probably reform them well enough to attach a short hose accessory of your choosing, then attach hoses to that going forward. I wouldn't continue to regularly use the threads as they'll be slightly weakened and prone to recurring damage.

Remember that hoses seal at the washer, not the threads, so condition needn't be perfect.

One option is a chaser (like a die), as shown here. Another would be a triangular file.

enter image description here

source

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    As a suggestion for the "short hose accessory," I'd recommend a quick disconnect. They're inexpensive and make it very easy to swap connections. Commented Jun 17 at 16:19
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That hose bib looks obsolete and damaged too. It's time for an upgrade.

If you're desperate to connect a hose, it will help to add an extra washer or two. That way it might seal without screwing up to the "normal" spot.

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    What does "obsolete" mean in this context? Not a criticism, just curiosity. Commented Jun 17 at 12:39
  • @EricHauenstein Trying to attach a vacuum breaker to a broken old hose bib when one could instead acquire a shiny new anti-siphon sillcock, makes that rusty old thing look fairly obsolete. Sorry I'm not so familiar with plumbing code. Commented Jun 17 at 14:00
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The threads are clearly damaged.

This zoomed in picture shows clearly uneven threads, which will most likely prevent you from tightening it fully to form a seal.

The other answers have suggestion on replacement or repair options.

enter image description here

This is what good looking threads should be like: enter image description here

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  • The damaged thread looks as if it gives an extra channel that water can leak passed even if a hose were threaded successfully.
    – civitas
    Commented Jun 15 at 17:34
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    @civitas As Isherwood says, hoses seal at the washer, not the threads. Commented Jun 17 at 11:39
  • The broken threads will most likely not thread properly to allow the seal to connect to the washer. Looks like someone forced incompatible threads through it and really chewed them up.
    – Nelson
    Commented Jun 17 at 13:04
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That's a taper thread, like NPT, not the straight thread NPS. Try to find a NPT hose fitting, or pack the thread with sealing thread or hemp.

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  • This may be the special threads that hose bibs had at one point in time which would not fit standard hose threads. These special threads fit the female threads in a type of vacuum breaker. The purpoe was to prevent direct connection of a hose and require that a vacuum breaker be connected. The male threds on the other end of the vacuum breaker were standard hose threads allowing connection of a standard hose. Commented Jun 16 at 1:30
  • +1. This answer is wrong for the OP but it has value for future askers of similar questions. Imagine a question with identical text but a picture of a ball valve with a 3/4" pipe coming off it. This might be exactly the right answer. Commented Jun 17 at 2:38

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