In the US and Canada, shower arms and heads use 1/2" NPT (also called 1/2" IPS), and in the UK, Australia and New Zealand 1/2" BSP (G1/2), which Australians often call 15 mm. The two aren’t the same thread, so a head from one needs an adapter to go on an arm from the other.
Where’s the shower?
What are you connecting?
Your shower thread
1/2" BSP (G1/2)
A parallel thread with 14 threads per inch, about 20.96 mm across. The washer in the head’s nut makes the seal, so it goes on hand tight.
On the package: 1/2 in. BSP, G1/2
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Your shower thread
1/2" BSP, often called 15 mm
Sold as 15 mm, though the thread is about 20.96 mm across. It’s parallel, with 14 threads per inch, and a washer seals it, hand tight.
On the package: 1/2 in. BSP, often called 15 mm
Available on Amazon
Your shower thread
Check the size printed on it
Outside the US, Canada, the UK, Australia and New Zealand, look for the thread size on the shower arm or the head’s box.
Start overYour shower thread
1/2" NPT
The tapered pipe thread on US and Canadian shower arms, 1/2" pipe (0.840" across) with 14 threads per inch. Makers also call it 1/2" IPS or standard 1/2" pipe.
On the package: 1/2 in. NPT, also sold as 1/2 in. IPS
Available on Amazon
Your shower thread
1/2" NPSM or G1/2, by maker
American Standard, Delta and Moen hand shower elbows take a 1/2" NPSM hose. Kohler’s take G1/2. Both are straight threads with 14 per inch, sealed by the washer in the hose nut.
On the package: 1/2 in. NPSM, or G1/2 for Kohler
Available on Amazon
See also
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NPT and BSP side by side
| 1/2" NPT | 1/2" BSP (G1/2) | |
|---|---|---|
| Used in | US, Canada | UK, Australia, New Zealand |
| Shape | Tapered | Parallel (straight) |
| Thread angle | 60° | 55° |
| Threads per inch | 14 | 14 |
| Across the male thread | About 0.83" (0.840" pipe) | About 0.825" (20.96 mm) |
| Seals on | The threads, or a washer in the head | A washer |
Because the angle and the shape differ, the two don’t screw together properly even though the size name and thread count match. To join them, use an adapter with one of each: 1/2" BSP female x 1/2" NPT male, or the reverse.
Tape or no tape?
On US heads, the makers disagree. Moen’s instructions say to wrap the shower arm with thread seal tape. Delta’s say to seat the washer in the head’s nut, tighten by hand, and skip tools and tape, which can make the head fail. Waterpik uses tape only where the arm connection is metal, never on a plastic one. Follow the sheet that came with your head, and take off any old tape and the old washer first.
On BSP heads and hoses, the washer makes the seal: hand tight, no tools and no tape at the head. Tape belongs only on the arm’s thread where it goes into the wall fitting.
Handheld shower hoses
A handheld shower’s hose threads depend on the maker: 1/2" NPSM or G1/2. See shower hose thread size. In the UK, Mira’s replacement hoses are 1/2" BSP at both ends, sealed by washers.
Joining a different pipe or fitting?
Pipe thread size