thread type confusion

[z5593176]

I recently bought a shower filter from amazon which claims to have 1/2" thread as per North American/ European standard (top in the image below). However, despite being the same radius as my shower's thread (bottom in the image, it is a Mildon All Directional Fixed Shower Chrome 3000AS if that is relevant), it does not screw in at all. I've attached an image below that shows both the thread types in their male form. I initially thought that the problem may be that the thread of the shower filter I purchased was BSP, and my home thread was NPT, since I went to the store to try on 15 mm threads, and they all worked with the shower filter, but none fit on my current shower head. I also brought out an old shower head I had and it screws on perfectly with the filter, but is unable to screw onto my current shower. Since I am in Australia and BSP is the standard, this would make sense. But the filter being in imperial units and North American/ European standard, would seem to suggest NPT? Or perhaps this is not the issue at all? I went into a bunnings but didn't receive much help. 

[JacobZ]

Hi @z5593176,

A warm welcome to the Bunnings Workshop community and thank you for your question.

Unfortunately, as neither of these products come from Bunnings suppliers, I am not able to follow up on them for details about the thread pitch. It would be worth contacting the producers of these products to ask what thread they use.

I'm struggling to understand a couple of things, so I'll ask a few questions.

Have you used this showerhead in your home without the filter? Did it work with your home plumbing?

I'm assuming the shower head comes on an arm. Is this correct?

Considering the threaded adaptor you tested worked fine with the filter and an old showerhead, the logical assumption is that the new showerhead is the issue. 

What I suspect is happening is the thread that attaches the shower arm to the wall is compatible with Australian plumbing, but the connection between the shower arm and the shower head uses a different thread, likely from the location where it is produced.

Unfortunately, I'm not aware of a way to adapt to this issue. The only suggestion I have is replacing the shower head and possibly the shower arm.

Let me know if you have any questions or thoughts.

Jacob