Making Pipe Threads Fit Closer Together?

[Koa]

I'm installing a Grohe Retro Shower System. It uses existing faucet and adds a diverted. It screws into existing shower arm fitting with a brass threaded fitting. Different length nipples are used to adjust length the brass fitting protrudes from wall to be within the small tolerance allowed. My in wall shower fitting is very close to the surface which means the shortest nipple is a close nipple. Basically the two fittings I’m connecting need to bottom out on one another. It seems like there’s no way to really make any adjustment to close nipple other than shortening it or sanding the threads a bit. Not sure if that would help on a tapered joint, plus not leak. I’m within about 1/8” too high. There won’t be much water pressure on fitting since it’s never shut off there. The other thing I’m concerned about is once I crank it down and it doesn’t tighten down enough is then getting it apart. I’ve installed five of these without running into this problem. This one is going on my shower so I can spend a bit of time on a solution. I’d rather not use two spacers to offset the entire unit from the wall. Sand/grind down close nipple and solder deeper into Grohe's fitting? Any ideas?

https://cdn.cloud.grohe.com/tpi/100...223.1512459419.1563914144-83155335.1563718177

 

[Reach4]

How about using a 1/2 NPT tap on each inside thread, and using pipe dope without tape? Maybe a bottoming tap.

 

[Sponsor]

 

[Koa]

How about using a 1/2 NPT tap on each inside thread, and using pipe dope without tape?

That would help by cleaning up the threads a bit? Would that make the threads deeper? I bet the tap would bottom out before helping much. Really concerns me to do anything with fitting in wall since I can’t repair that without breaking into tile.

 

[Reach4]

Yes, it should clean out the threads.

At 14 tpi, 1/8 inch is less than one thread on each side. So not a lot of cutting would be needed. If you overdo it a tad, add PTFE tape.

I have used an NPT die to shorten nipples for fine tuning. In that case, I put the die on the thread before grinding off the tip. I don't know how that would work out with a close nipple. I have not had good luck with inside pipe wrenches.

 

[Cjlambert]

Buy a 1/2” running thread nipple. Cut a piece ¾” long (⅜” engagement for both fittings), and apply a liberal amount of t-tape.

 

[Koa]

Buy a 1/2” running thread nipple. Cut a piece ¾” long (⅜” engagement for both fittings), and apply a liberal amount of t-tape.

Thanks for that. Will try that if I can find it. Been searching online and found a couple places selling stainless. Would rather have brass. If you know of a place that sells it please post.

 

[Cjlambert]

Thanks for that. Will try that if I can find it. Been searching online and found a couple places selling stainless. Would rather have brass. If you know of a place that sells it please post.

Any local plumbing supplier will stock running thread brass nipples.

 

[hj]

that's interesting, because I do NOT KNOW of any, nor have I ever heard of anyone stocking them.

 

[Koa]

that's interesting, because I do NOT KNOW of any, nor have I ever heard of anyone stocking them.

None of ones near me carry them. Found a valve for a washing box that has running threads I can cut off. $15 from Home Depot if all else fails.

 

[Koa]

Ended up cutting the valve threads off. Seems to work fine although there’s no way to really test it. These really are great units for $300.