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 Shower arm not threading into new drop 90 in shower wall?
Author: GregD1 (AZ)

So I just got finished rebuilding my entire shower from the pan/walls up and tilework is complete. My buddy, who does showers for a living helped me install the new plumbing. The standard shower arm from Lowe's will only thread into the drop 90 in the wall about a half a turn before it gets very hard to turn. The strange thing is that the test plug still goes in easily without effort. I tried both sides of the shower arm and neither will work. I also insured that the shower arm will fit into a standard shower head that I bought separately and it fits easily. The test plug also threads perfected into the shower head. I do not see any visible signs of cross-threading and I have no pipe dope or tape on the threads yet. Any thoughts here or suggestions to try?

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 Re: Shower arm not threading into new drop 90 in shower wall?
Author: Lorensr (CA)

You might need to take a small metal chisel and open the hole by 1/16". That is normally all it takes. Use a new 1/2" galvanized nipple to clean out any possible cross threading that may be present

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 Re: Shower arm not threading into new drop 90 in shower wall?
Author: bsipps (PA)

I’ve had this issue with big box store shower arms, get a name brand shower arm from your local plumbing supplier or our sponsor plumbingsupply.com

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 Thank you clap
Author: GregD1 (AZ)

Thank you both for the replies. I will run to the plumbing store first and then try the other method if not. Appreciate it.

Edited 2 times.

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 Re: Shower arm not threading into new drop 90 in shower wall?
Author: sum (FL)

what is the material of the drop 90 inside the wall? Brass or CPVC or something else? Is the drop 90 secured to the framing or yielding a bit? Could the issue be a slight difference in the angle of entry?

Is the test plug that works metallic or plastic?

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 Re: Shower arm not threading into new drop 90 in shower wall?
Author: hj (AZ)

YOu have a badly threaded shower arm.

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