Why can't I connect a hose to this outdoor faucet?

Question

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.

Answer 1

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.

_source

Answer 2

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.

Answer 3

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.

This is what good looking threads should be like:

Answer 4

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.