Ok,tried to reduce 3/4 steel nipple to 1/2, with galv reducer and 1/2 nipple into that....coupling only goes on a few turns, so didn't force it. Is this a straight thread/tapered thread thing? My untutored guess is that faucet inlet is meant only for a compression fitting? (Am doing the reduction because the supply line is half inch pex with a half inch swivel elbow, and no one carries a swivel elbow that joins a 1/2 barb with 3/4 FPT swivel. Any help appreciate d.

The faucet supply should be ½" straight pipe and would use a compression seal. Are there stop valves installed for this faucet? You normally wouldn't pipe the supply lines directly to the faucet.

Thanks. It's a clawfoot tub with 3/4 in. faucet inlets. There was no plan for a stop valve, because the pex manifold is nearby and handy. I wanted to run the 1/2 pex up to the 3/4 in. inlet but I guess that's not the done thing because no one carries a 1/2 to 3/4 coupling. So I was trying to reduce the inlet nipple, as the OP described. Since posting, I learned that you can get a braided steel flex line with a 1/2 to 3/4 fitting, designed for clawfoots, which can make the bend, so I think I'll just go with that and damn the expense.

I was thinking you were installing a sink faucet. I don't know what threads your tub valve has or what you need to connect it.

Let me clarify, and maybe increase my understanding (and that of other lay readers) of threads (which confuses the ___ out of me). The tub needs a faucet installed and the inlets are 3/4 inch, and have a NPS (National Pipe Straight) thread so that a watertight seal can be made with a compression fitting. I can do two things to deal with these 3/4 inch nipples in a house served by 1/2 inch. PEX supply lines:

1. I can directly attach a 3/4 inch compression fitting, as on the end of a specialized flex line. The other end of the supply line has a 1/2 compression fitting. This specialty line is not cheap. I need two. So....

2. I can somehow reduce the 3/4 inch nipple to a 1/2 inch NPS nipple, if I can somehow find the right kind of coupling(s). Since no one seems to carry a reducing coupling that is female 3/4 NPS on one end and 1/2 male NPS on the other, I would therefore have to buy an all-female reducer coupling (NPS) and then put the faucet nipple in one end and the 1/2 inch. extension in the other.

To implement (2), I realize I must "refrain from asking where to purchase a product," so I'll just ask if there is a way to put the correct thread information into a search engine and find my way to the correct couplings. I already stumped the guy at Lowe's, which isn't that hard to do, frankly.

Depending on the visual aspect of this installation, there are flexible connectors for water heaters, in corrugated stainless steel or copper, or braided stainless steel. Those would seal against the ¾ NSP at the faucet and would seal to a ¾ male fitting at the Pex end.

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