Shower head thread size in the UK: what 1/2 inch BSP means

The usual shower head thread size in the UK is 1/2 inch BSP (British Standard Pipe). Two major UK shower makers say their replacement hoses use a standard 1/2 inch BSP connection. The thread measures about 21 mm across, not half an inch, and some showers have a 3/4 inch connection, so check yours before you buy.

This guide explains what the size means, which hose nut goes where, where the washer sits and how to measure your own outlet before you buy a head or hose. For the wider picture, read our guide to filter shower heads in the UK.

We sell a filter shower head kit, so every size and rule here links to its source.

What is the standard shower head thread size in the UK?

The usual shower head thread size in the UK is 1/2 inch BSP, used by most showers and hoses. The main exception is a 3/4 inch connection, which some showers have.

A shower hose buying guide from one major UK shower maker (December 2021) says most showers have a 1/2 inch connection and most hoses are made with that in mind. It adds that some showers have a 3/4 inch connection, so check before you buy, and that all of that maker's hoses have a standard 1/2 inch BSP connection.

Another major maker's shower hose page says its hoses use standard 1/2 inch BSP connections, and that almost all of them suit most showers and shower heads.

So a head or hose made to 1/2 inch BSP will usually screw onto a UK shower. Usually is not always: the nut, the washer and your shower's own rules still decide whether it fits, and the sections below cover each.

What does 1/2 inch BSP mean?

BSP means British Standard Pipe, and the 1/2 inch in 1/2 inch BSP is a nominal size, not a measurement. A 1/2 inch BSP thread is about 21 mm across the outside, with 14 threads to the inch.

A thread identification guide from a pipe-fittings maker lists the parallel form, BSPP (British Standard Pipe Parallel), under the international standard ISO 228-1. For the 1/2 inch size, its February 2025 edition gives a nominal outside diameter of 20.96 mm, 14 threads per inch and a 55° flank angle.

In the UK that standard is published as BS EN ISO 228-1:2003, which the British Standards Institution (BSI) lists as current. Its title spells out the key point for a shower: these are pipe threads where pressure-tight joints are not made on the threads.

Other thread standards can look almost identical. The same fittings guide shows that the American NPT thread also has 14 threads per inch at the 1/2 inch size. But NPT is tapered and has a 60° thread angle, so it is a different thread, not a version of BSP. If a head or hose is sold for another market, check that the listing says 1/2 inch BSP.

Conical nut or flat nut: which end of the hose goes where?

On many UK shower hoses, the conical nut goes to the shower head and the other end screws onto the shower outlet. That other end may be a second conical nut or a plain, straight-sided nut, sometimes called a flat nut.

The second maker's hose page gives the simplest rule: fit the conical end of the hose to the shower head. A third maker's product details for one of its hoses list a cylindrical nut on the fitting side and a conical nut on the hand-shower side.

Not every hose has two different ends. The first maker's 2017 fitting guide for one of its shower kits puts a hose seal into a conical nut at each end: one on the shower outlet, one on the handset.

Cones are not all alike either. The same maker's guide to replacing a shower hose (June 2023) says the cones on hose ends can differ, which affects how the hose fits a riser rail or bracket. With the wrong one, the hose is tricky to fit and the head may slip during a shower.

So compare both ends before you buy, or take the old hose to the shop, as the buying guide above suggests. Choosing a whole new hose? Our guide to replacement shower hoses covers length and material.

Where does the washer go, and does the thread seal?

The washer sits flat inside each hose nut, and the washer, not the thread, makes the seal. A parallel BSP thread holds the joint together, while the washer, squeezed between the nut and the end of the outlet, keeps the water in.

BSI's summary of BS EN ISO 228-1 says these parallel threads are intended for the mechanical assembly of fittings. If such a joint must be watertight, it says, that should be done by compressing two surfaces outside the threads with an appropriate seal between them.

That is why hose guides are precise about washers. The hose replacement guide says to put the washer into the end of the new hose that connects to the water outlet, then screw it on clockwise until hand-tight. The same goes for the shower head end, and a washer in good condition can be reused.

Tightness matters as much as the washer. The same guide warns that over-tightening could break the washer or damage the thread. An electric-shower maker's installation guide (September 2025) says finger tight is sufficient for the hose and shower head connections.

PTFE tape isn't the seal either. Use it only if a threaded joint still drips once a good washer is in place and the nut is hand-tight: a few turns on the outlet thread, wound the way you screw, as our step-by-step guide to fitting a shower head and hose explains. Tape can't make up for a missing or worn washer.

How to check your shower's thread before you buy

Checking a shower's thread needs the manual, the old hose and a ruler: read the specification, unscrew the hose, look at both nuts and measure the outlet. A 1/2 inch BSP outlet measures about 21 mm across the outside of the thread.

1. Read the manual. The specification table may list the outlet connection: the 2025 electric-shower guide above, for example, gives a 1/2 inch BSP male thread.
2. Unscrew the old hose. With the shower off, turn the nut anti-clockwise by hand, and keep the washer: the hose replacement guide warns not to lose it. If the nut won't move, read what to do when a shower head or hose is stuck.
3. Look at both ends. Note which nut is conical, which end sat in the holder and whether each nut has a washer inside.
4. Measure the outlet. Hold a ruler or callipers across the outside of the thread and compare the reading with the table below.
5. If in doubt, take the old hose with you. The buying guide suggests measuring the old hose or taking it to the shop.

The figures are nominal diameters from the fittings maker's thread guide, which notes that measured threads may not match a table exactly because all threads have tolerances. At 14 threads per inch, you can also count the threads along 25.4 mm of the outlet as a second check.

Do you need a shower hose adaptor?

A shower hose adaptor is only needed when your outlet and your new hose or head don't match, for example a 3/4 inch outlet and a 1/2 inch hose. An adaptor is no fix for an electric shower whose manual allows only the maker's own hose and head.

An adaptor adds a joint, and each joint usually needs its own washer and a straight, hand-tight start. If you need one, ask the maker of your shower which adaptor, if any, it allows, and follow the instructions that come with it.

On an electric shower, don't add anything at the outlet. The 2025 electric-shower guide says the outlet acts as a vent and must not be connected to anything other than the hose and shower head supplied. The 2017 fitting guide adds that no flow control should go in the outlet pipework of a shower, such as an electric one, that needs its fittings to act as a vent.

Weighing up a filter head for an electric shower? Waterhush is not for electric showers unless your shower's manufacturer confirms in writing that a filter head can be fitted to your model; read what electric shower manuals say about replacement heads first.

What a thread check can't tell you

A thread check tells you whether a nut will screw on, not whether a head suits your shower. Your shower's rules, your flow and your holder decide that, and none of them shows up on a ruler.

• Your shower's rules: some electric shower manuals allow only the maker's own hose and head, whatever the thread.
• Flow: a thread size says nothing about how much water reaches the head. If your flow is already weak, check your manual before choosing any head.
• Your holder: cones and handles differ, so a head can fit the hose and still sit loosely in its holder.
• Fixed heads: this guide covers hoses and handheld heads; a fixed head on a shower arm needs its own instructions.
• Tolerances: a measured thread won't match a table exactly.

Our own kit's thread size isn't confirmed yet, so we can't promise it will match your outlet. We would rather say so than guess.

Waterhush and your outlet

The Waterhush Shower Kit comes on its own 1.5 m hose, with one washer and PTFE tape, so the joint that matters is your shower's outlet. The kit's thread size isn't confirmed yet, so we can't say it will match your outlet; if you're unsure, contact us before you buy.

The kit also needs a shower with a hose outlet: a handheld head on a flexible hose, not a fixed head only. Waterhush is not for electric showers unless your shower's manufacturer confirms in writing that a filter head can be fitted to your model.

Before you buy, our three-question check covers the basics, though it can't confirm the thread.

The bottom line

Most UK showers and hoses use a 1/2 inch BSP thread, about 21 mm across, and the washer in each nut makes the seal. Some showers use 3/4 inch, and some electric showers allow only their maker's hose and head, so a matching thread is not the whole answer. Read your manual, measure the outlet and compare both hose ends before you buy.