The supply connections listed at the website do not show any connections for NPT threads. Did you screw the PEX adapter onto the brass nipple of the box? Those nipples are not tapered, not NPT. The taper provides the sealing.

Here is a link that might be useful: Ox box

The threaded supply connectors are listed as "ý" female sweat". They did not look like NPT threads, but then what do you thread onto them if you want to connect a PEX adapter? There is another version of the Ox Box with PEX supply connectors, but none of the stores stocked them.

I went back to Home Depot and they sold me some gray teflon tape that they said would work better to seal the threads. I figured out how to get a wrench to hold the Ox Box fitting and then tightened down the PEX adapter tight enough so that it would not leak. It is holding well, but I don't want to close up the wall if its not the right type of connection.

Bruce

You should have investigated the meaning of the the words 1/2" female sweat. The box was designed for a 1/2" copper pipe to be inserted into the brass nipple and soldered-- with all the proper steps involved in that process.
What did you think those words meant?

Bus_driver - It appears you are much smarter than I am in this area. However, your comment only makes sense if there was a nipple to solder onto. The supply fitting is a 1/2" male threaded fitting and there is no copper pipe that would accept a standard 1/2 copper fitting. Are you saying I should somehow solder a copper pipe onto or into a threaded fitting?

Bruce

Watch and see what I described at about 1:30. Looks as if it is time for you to hire a pro.

Here is a link that might be useful: animation

This post was edited by bus_driver on Sat, Jan 10, 15 at 12:17

So I guess you don't know anything about the outside threads and what they are supposed to be used for? The video does not show any connection to threaded fittings, and the since its a cartoon picture you can't even see the outside threads.

The supply pipes can be soldered inside the fittings, so I guess the outside threads only serve the purpose of holding the fittings in the box.

Bruce

"The supply pipes can be soldered inside the fittings, so I guess the outside threads only serve the purpose of holding the fittings in the box."

Perhaps the concept is becoming clear.

The installation you have done thus far was never intended by the manufacturer. It may be leak-free for a very long time-- or not.

For the Ox Box the outside threads hold the fitting in the box, so they have an additional purpose. However, I also have a freeze proof hose bib and Delta shower valve that have 1/2" threads on the outside and are sized inside for a solder connection.

Both of these other devices (shower valve and hose bib) are designed so that you can disassemble and remove all the plastic and rubber parts when you solder, so there should be no problem with excessive heat. The video from Ox Box shows someone soldering them with the valves installed, so it appears that the valves are more heat resistant, or the stems are long enough to let them hold up to soldering while in place. However, I will probably at least pull them out of the plastic box while soldering on the connectors.

Bruce