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I was replacing my kitchen faucet when I ran into an issue that I didn't foresee (yes, this is my fault for not looking ahead!). The supply lines attached to the faucet and the supply lines coming from the angle stop do not connect together (two female ends) and are of different sizes. The water supply lines have 1/2 inch female connectors and the lines coming from the faucet have 3/8 inch female connectors. What's more, the supply lines from the angle stop are crimped to the stop and can't be easily removed.

1/2 inch female flexible supply line coming from angle stop 1/2 inch female flexible supply line

3/8 inch female flexible supply line coming from faucet 3/8 inch female flexible supply line

angle stop with crimped supply line (the other end is the 1/2 inch female hex connector) angle stop with crimped supply line

Now, what I would like to do is connect these supply tubes to each other because there is not an easy way for me to replace the stops, uncrimp the water supply lines, or remove or replace the faucet supply lines.

I believe my question is similar to this one.

Connect 1/2" supply line to 3/8" outer diameter faucet line

Unfortunately, I am unsure of the appropriate diameters to consider when purchasing something because I do not know if the connectors on my lines are NPT (taper) threaded or compression (parallel) threaded.

I have seen there are adapters like compression unions and reducing nipples, but I am unsure of which kind to buy or if there are any for my situation. Another idea I had was to join the two lines using another angle stop, such as the one below, but I am also unsure if that would work or even be a sound solution.

1/2 in. Nominal Compression Inlet x 3/8 in. O.D. Compression Outlet Multi-Turn Angle Valve

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Get 3/8" male to 1/2" male nipple.

Note you need two wrenches and one of these:

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One wrench on the hex nipple, one wrench on the hex female nut, and the pliers above to hold the crimped part of the flexible pipe to prevent it from turning. If the flexible pipe turns, it'll either unscrew from below the socket and you'll get a leak, or it'll bend at awkward angles which will damage the stainless steel weave (that might cause it to burst after a few years) or crush the internal rubber pipe so you get less water flow.

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  • I agree with you that there shouldn't be any attempt to turn the crimped part, but I'm not sure that it really needs to be held. Turn the nipple into the supply line until it's finger tight, then one wrench on the free brass nut on the supply line and another on the nipple - hold the nipple still, turn the nut. The nut should spin freely on the supply line. Besides, where's that third hand going to come from?
    – FreeMan
    Nov 15, 2021 at 12:43
  • When you turn the nut, the flexible pipe usually wants to turn along with it. It's doable with 2 hands.
    – bobflux
    Nov 15, 2021 at 13:06
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    @Dorik you'll need wrenches to tighten the spinning nuts onto the nipple you pick up. I agree that you'll want to be careful to not twist the flex lines, but I don't think you'll need the 3rd wrench. I've tightened these flex lines onto faucets and toilets and not had issues with them binding/twisting at the other end. bobflux does think you'll need it a 3rd wrench to prevent that from happening. I think the best thing is for you to be careful as you tighten and be prepared for the line to start twisting and STOP if it does and reassess your procedure from there.
    – FreeMan
    Nov 15, 2021 at 14:03
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    Don't fit any of this without using ptfe tape. Since they're not tapered, they will screw to the end, and will potentially leak. Ptfe will make the joint watertight. I sometimes end up using a washer to screw down onto as well.
    – Tim
    Nov 15, 2021 at 15:04
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    @Tim Both of the hoses have a rubber washer visible inside them. They also have swivel nuts. Both of these are signs that threads aren't the sealing surface (with a compression type fitting, the thread is never the sealing surface). Therefore PTFE tape or pipe dope are unnecessary. If a compression or washer/gasket/o-ring sealed joint leaks it's either not tightened properly or is physically damaged and should be replaced.
    – Greg Hill
    Nov 15, 2021 at 19:03

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