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?

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

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

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.

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?

YOu have a badly threaded shower arm.