Dimensions and pipe connections: what do 1/2", 3/4" and center distance mean

We are still preparing products.

But you can look at other categories.

Dimensions and connections of taps: what do 1/2", 3/4", and center distance mean

You buy a nice-looking tap, come home, start installing it – and suddenly you find out that the threads don't fit, the hoses are too short, or both connections stick out where there should be only one. This is not a rare situation. It is one of the most common reasons why customers return to the store or call a plumber even before the new tap has let out a single drop of water. The problem is not in a bad tap – the problem is that most people when choosing focus only on design and price, and skip the connection dimensions as a boring technical detail.

This article will explain that "boring technical detail" in depth – what threads are used, what the inch markings exactly mean, why a center distance of 150 mm is not the same as 152 mm, where these dimensions are physically located on the tap and on the installation, and how to measure everything correctly before purchasing. If you want to be sure of your choice and avoid unnecessary trips with returned goods, read on.

Why connection dimensions are so important

A plumbing tap is not a standalone object – it is part of a whole system. It must fit into the installation in the wall or on the sink, must be connected to the hot and cold water supply, and in the case of wall-mounted installation, it must pass through a hole of the correct size. When these three conditions are not met simultaneously, the tap simply cannot be mounted or will leak.

In practice, we most often encounter these problems:

The customer buys a tap with 1/2" outlets, but the wall has old copper pipes ending in a 3/4" thread.
The tap has a center distance of 150 mm, but the existing wall outlets are 120 mm apart – the tap cannot be connected without renovation.
The hole in the sink is 35 mm, but the tap requires a 38 mm hole.
The attached flexible hoses are too short, the customer buys longer ones, but forgets to check whether they have the same type of fitting.

None of these problems are technically complex – but each of them requires that you know what to look for even before purchasing.

Inch threads: what does 1/2" and 3/4" mean

Plumbing taps use threads according to the BSP (British Standard Pipe) standard, sometimes also called G-thread. It is an old British standard that is still used throughout Europe despite the metrication in construction – simply because it has become deeply rooted in the entire installation system and changing it would be too expensive.

The basic markings look like this:

G 1/2" – external thread with a diameter of 20.955 mm, 14 threads per inch
G 3/4" – external thread with a diameter of 26.441 mm, 14 threads per inch
G 1" – external thread with a diameter of 33.249 mm (less common for taps)

An important fact that surprises many: the inch number does not correspond to the actual external diameter of the thread. It is a historical remnant from the time when an inch denoted the internal diameter of the pipe through which the water flowed. The thread itself is always larger. So when you see the marking 1/2", it does not mean that the thread has a diameter of 12.7 mm (which would be the actual half-inch). It has a diameter of almost 21 mm.

Practical implication: never measure the thread with a caliper and directly compare the result with the inch number. Always look for the marking on the tap or in the catalog sheet, or measure the thread and compare it with the BSP dimension table.

External thread vs. internal thread

With taps, you will encounter both types. External thread (marked with the abbreviation „V“ or in English „male“) is a thread that is screwed into something – for example into the body of a wall-mounted installation or into a reducer. Internal thread (marked „V“ or „female“) is a thread into which a hose or connector is screwed.

A typical case of a wall-mounted tap: the outlets pointing downward have a internal thread of G 3/8", into which the connecting hoses (flexi) are screwed. The hoses have an external thread on both ends – one end 3/8" (to the tap), the other end 1/2" (to the angle valve). This is a standard combination for most modern wall-mounted taps.

So if you see „connector 3/8"“ somewhere in the technical documentation of the tap, it refers to the thread to which the flexible hoses are connected – and not the thread with which you would connect the tap directly to the pipe in the wall.

Where 1/2" and 3/4" are actually used

The thread G 1/2" is by far the most common for wall-mounted taps on sinks, basins and bidets. It is the standard for most modern bathroom and kitchen taps. Flexible hoses with 1/2" ends (on the side of the angle valve) are commonly available and cheap.

The thread G 3/4" typically appears in:

Bathtub taps – a higher flow requires a larger diameter
Shower systems with multiple outlets
Garden taps and outdoor outlets
Older installations (especially copper and steel pipes from the socialist era, where 3/4" pipes were standard)

Exactly the combination of old 3/4" pipes and a new tap with a 1/2" connector is a source of many problems during renovations. The solution is either a 3/4" → 1/2" reducer screwed onto the angle valve, or the purchase of flexible hoses with different ends on each side (3/4" × 1/2" or 3/4" × 3/8").

Center distance: what it is and why it matters

Center distance (sometimes also called "tap spacing") is the distance between the centers of the hot and cold water outlets. You measure it from the center of one outlet to the center of the other, horizontally – not along the surface of the wall, but in a straight distance.

Why is this important? Because a wall-mounted or bathtub mixer with fixed outlets must be installed exactly at the distance the mixer has. If the center distance of the wall outlets is 150 mm and you buy a mixer with a center distance of 120 mm, the mixer will simply not fit. The outlets will not be aligned – and even flexible hoses will not elegantly compensate for this difference, because they would have to go diagonally and would not withstand pressure testing.

Standard center distances

In practice, we encounter these values:

150 mm – European standard for bathtub mixers and shower sets (DIN EN 1102), by far the most common
120 mm – used in some shower and basin mixers, less common
100 mm – occasionally found in older or smaller installations
76 mm – typical for sink double taps (so-called "kitchen stand" with separate taps)

The outlets of a stand mixer (basin or sink mixer) are mostly flexible hoses – so with stand mixers, the center distance is less critical, as the hoses can be bent. But even here, there are limits: if the angle valves are too close to each other or too far apart, the hoses may be too strained or twist awkwardly.

How to measure the center distance on an existing installation

Before buying any bathtub or wall-mounted mixer, always measure the distance between the outlets. Use a tape measure and measure from the center of one outlet to the center of the other. If they are covered by caps or covers, carefully remove them and measure from the center of the threaded outlet.

Watch out for tolerances: in built-in installations (e.g., rough-in), a deviation of ±5 mm is common – most mixers have some movement or adapter on the connections to compensate for this. If the difference is larger (e.g., 15 mm), you will most likely need to modify the installation or use special eccentric connections.

Eccentric connections (eccentrics) are threaded adapters between the wall and the mixer, allowing to compensate for an axial deviation of ±15 to 20 mm. They are a standard part of the packaging of most bathtub mixers and are practically irreplaceable in built-in installations. However, some mixers do not include them – so always check what is included in the packaging.

Hole diameter in the basin or sink

For a stand mixer, you need not only the correct threads but also the correct hole in the basin or sink. The standard diameter for a single-hole stand mixer is 35 mm, and the mixer usually has a sealing washer (rubber gasket) and a fixing nut from below.

Some mixers (especially design models with a larger base) may require a hole of 32 mm or 38 mm. If you are buying a mixer for an existing basin, always check the hole diameter in the basin before deciding on a specific model. If you are buying the basin and mixer together, you can choose the combination according to your preference.

For double-hole sink mixers (hot and cold separately), the distance between the holes follows the same logic as the center distance in wall-mounted mixers – most commonly 76 mm, but it may vary according to the sink manufacturer.

Concrete examples from practice

Example 1: Bathroom renovation, bathtub mixer

A customer is renovating an old bathroom. The original bathtub mixer was built-in, the masonry grout had dried, and the tiling is new. The outlets from the wall are new plastic pipes with a G 1/2" thread, placed 150 mm apart. The customer chooses a bathtub mixer without accessories from ARKO in satin finish. The packaging includes eccentrics, seals, and covers. The eccentrics compensate for uneven outlet seating (the left one protrudes 8 mm more than the right one), and the customer simply adjusts them before tightening the mixer permanently.

Example 2: Replacing a kitchen sink mixer

A housewife wants to replace an old sink mixer. She has a sink with one 35 mm hole. Under the sink are angle valves 1/2" installed on copper piping. She buys a sink stand mixer from ARKO in satin finish. The mixer has G 3/8" outlets (internal thread) – flexible hoses 3/8" × 1/2", 35 cm long, are needed. The flexible hoses are not included in the packaging, and the customer buys them separately. The installation is done by hand with a wrench and hose pliers – the entire procedure is described in detail in our article Installation of a water mixer: procedure, tools, and common mistakes.

Example 3: Bidet mixer with drain kit

A customer is installing a bidet with a drain kit. The bidet has a 32 mm hole, the angle valves are 1/2", and the height of the outlets above the floor is 220 mm. A bidet mixer with a drain kit from ARKO in chrome finish has a standard 32 mm spout diameter and flexible hoses in the packaging with 3/8" × 1/2" ends. The mixer is fixed with a nut from below, and the drain kit is connected to the trap. The customer checked that the mixer has an internal thread on the drain outlet G 5/4" – which is standard for bidet drains. More about what is included in the packaging and what needs to be bought separately can be found in the article Bidet mixer with drain kit: what is included in the packaging and what needs to be bought separately.

Example 4: Old apartment, 3/4" piping

A panel apartment bathroom from 1978. The piping is steel, with a 3/4" external thread. The customer wants to install a modern single-hole basin mixer. The new mixer has G 3/8" internal thread outlets – standard flexible hoses 3/8" × 1/2". Problem: the 3/4" angle valve does not fit the 1/2" flexible hose. Solution: a 3/4" internal × 1/2" external angle valve (reduced angle valve) is directly screwed onto the old 3/4" external thread, or a standard angle valve with a 3/4" → 1/2" reduction. This is a common situation in the renovation of old apartments and plumbers deal with it daily. A customer doing the work themselves must have this detail planned in advance – otherwise, they will end up at the hardware store on Saturday evening with a leaking bathroom.

Flexible hoses: length, diameter and material

Flexible hoses (connecting hoses) are an overlooked detail that people deal with last – and yet they are the basis of the entire connection. A few practical rules:

Length: measure the distance from the battery outlets (from below) to the angle valve and add 5–8 cm for the bend. Common lengths are 30, 35, 40, 50 and 60 cm. A hose that is too long will sag and look bad, while one that is too short is dangerous – it can tear when moved.
Fittings: most commonly 3/8" on the battery side and 1/2" on the angle valve side. There are also combinations such as 1/2"×1/2" or 3/8"×3/8" – always check.
Material: braided stainless steel is more reliable than plastic. Do not buy hoses without metal – they will not withstand pressure and UV.
Seals: most hoses have a flat rubber sealing washer in each end. If the seal is lost or damaged, the hose will leak.

Although this may sound trivial, faulty or low-quality flexible hoses are one of the most common causes of water leaks under the sink or countertop. More on this in the article Common faults in water taps: dripping, weak flow, corrosion.

Wall-mounted tap: different logic of dimensions

With wall-mounted taps, different rules apply than with deck-mounted taps. Here, the tap is not a "standalone piece" with a solid body – instead, you have a built-in body in the wall (rough-in) and only the control part and outlets are visible on the surface of the wall. Dimensions are handled differently here:

Embedment depth: the body must be installed to a certain depth from the surface of the tile (usually 45–65 mm) – this is determined by the specific instructions from the manufacturer of the wall-mounted body.
Outlet axis distance: with wall-mounted bodies, it is fixed by the manufacturer, usually 150 mm or 120 mm.
Dimensions of the cover plate: the visible cover must sufficiently cover the hole in the tile and at the same time must not overlap with another element.

More on choosing between wall-mounted and deck-mounted taps can be found in a separate article Wall-mounted vs. deck-mounted tap: which is suitable for your bathroom.

Summary of key dimensions to find out before purchasing

Whether you are buying any type of tap, before purchasing, find out and write down the following information:

Mounting type: deck-mounted (hole in the sink/countertop) or wall-mounted/wall-embedded
Diameter of the mounting hole (for deck-mounted taps): typically 35 mm
Axis distance of T/S supply (for wall-mounted taps): measure on the existing installation
Thread of existing connections: 1/2" or 3/4" (external or internal)
Height of angle valves above the floor (for deck-mounted taps): affects the length of the flexible hoses
Contents of the package: flexible hoses? Eccentrics? Seals? Fixing nut?

This information will save you an unnecessary trip to the store and potentially one unpleasant situation with water leaking where it shouldn't.

Surface finish and dimensions: a connection people overlook

When choosing a tap, people consider dimensions and design separately, but in reality, they are connected in one practical aspect: different surface finishes can slightly vary the outer diameter of the tap spout. For example, satin or black matte finish can be slightly thicker than chrome – in most sinks, this does not matter, but in a sink with a precisely milled 35 mm hole, even one millimetre can be a problem. Always check the diameter of the spout in the tap's catalog. More on finishes can be read in the article Tap surface finishes: chrome, satin, black matte – differences and durability.

For example, the LOOP deck-mounted tap has a spout with a diameter of 35 mm and is designed for standard holes in sinks – if, however, you have an older sink with a 32 mm hole, you need to confirm this before ordering.

What to do if the dimensions don't match: practical solutions

Not always can you buy exactly the tap that fits perfectly without any modifications. In practice, the following solutions are most commonly used:

Thread reductions: metal or bronze reductions allow bridging the difference between 3/4" and 1/2". They cost a few euros and save hours of work.
Eccentric adapters: compensate for an axial offset of ±15–20 mm on wall-mounted taps. They are a standard part of most bath taps.
Extending nipples: a short metal piece with external threads on both sides, usable when the outlet is too recessed in the wall.
Flexible hoses with different ends: solve most differences between tap connections and angle valves – but only if you stay within standard dimensions (3/8", 1/2", 3/4").
Renovation of the installation: if the offset is too large, especially with fixed steel or copper pipes, there is sometimes no other option. A plumber can modify the outlets – usually within one working day.

If you are planning a bathroom or kitchen renovation and are unsure whether your installation fits a specific tap, the safest approach is to consult a plumber before purchasing. If the plumber knows which tap you will have, they can adjust the pipe outlets directly to it – and you will save hours of solving mismatches.

Bidet taps: a special case

Bidet taps have one extra compared to standard sink taps: a drain outlet (drain). This is a thread to which the pull-chain assembly controlling the trap in the bidet drain is connected. The standard thread here is G 5/4" external. This dimension is very specific and even experienced fitters should not confuse it – it is significantly larger than 1/2" and smaller than 1".

Bidet tap with drain assembly ARKO in satin includes the drain assembly directly in the packaging – which is convenient because its end is specifically designed for the exact outlet size and the customer does not have to search for compatible parts separately. Nevertheless, it is always recommended to verify that the trap of the bidet basin has the correct inlet size for the drain assembly valve.

Frequently asked questions (FAQ)

What is the difference between G 1/2" and R 1/2"?

G (or Rp) denotes a cylindrical (parallel) thread – sealing is achieved with flat gaskets or Teflon. R denotes a conical (tapered) thread, which seals itself when tightened. In practice, in the European context of water taps and connections, the cylindrical G-thread is dominant. The conical R-thread is more common in industrial environments. Interchangeability is partial – a G 1/2" external thread can be screwed into an Rp 1/2" internal thread, but sealing must be supplemented with Teflon or a flat gasket. Never mix them without sealing, as water leakage is likely.

Can I connect a tap with a 3/8" outlet to a 1/2" angle valve without a special hose?

Not directly. You need either a 3/8" × 1/2" flexible hose (one end 3/8", the other 1/2"), or a 3/8" to 1/2" reducer. Flexible hoses with different ends are commonly available and are a standard solution – that's exactly why they are produced. Directly screwing a 3/8" thread into a 1/2" internal thread would damage the thread and the connection would leak.

The center distance on my tap is 150 mm, but the outlets in the wall are 130 mm. What should I do?

A difference of 20 mm is on the edge of what standard eccentric fittings (adapters with adjustable extension) can compensate. First, try the eccentric fittings, which most bath taps include in the packaging. If the tap does not include them, buy separate G 1/2" eccentric adapters – they allow compensating for a deviation of up to ±15–20 mm on each side. If the difference is greater or the eccentric fittings are not enough, it is worth calling a plumber who can slightly move the outlets from the wall.

How can I determine what thread I have on the wall without using a caliper?

The simplest method: match the thread with a standard connection element (e.g., an angle valve or a reducer) that has a declared size, and try to manually – without tools – screw it in a few turns. If it goes in smoothly and easily, the size matches. If it is harder than it should be, it is a different size. Note: if it is too loose, the thread is either a different size or damaged. Alternatively, measure the external diameter of the thread with a caliper and compare it with a table: G 1/2" ≈ 20.96 mm, G 3/4" ≈ 26.44 mm, G 3/8" ≈ 16.66 mm.

Why does my new tap include gaskets in the packaging? Are they necessary?

Yes, they are necessary – and none should be skipped. Flat rubber gaskets (usually silicone or EPDM) are inserted into each threaded connection in flanged (pressure) sealing. Without gaskets, the connection will leak even with proper tightening. Some connections (e.g., external conical threads) are sealed with Teflon (PTFE tape) instead of flat gaskets – always follow the instructions included with the tap or with the hoses. For more on common installation errors, see the article Installation of a water tap: procedure, tools and common mistakes.

Can I buy a 3/4" tap for a sink if I have old 3/4" pipes in my apartment?

Most modern sink taps have outlets of G 3/8" or G 1/2" – not G 3/4". The solution is not to buy a rare 3/4" tap, but to install a reduced angle valve: 3/4" internal thread (on the pipe side) × 1/2" external thread (on the hose side). These angle valves are commonly available and cheap. Installation is simple and the whole system will work reliably. If you do not want to replace the angle valve, you can also use a 3/4" to 1/2" reducer directly screwed onto the existing angle valve – this is also a functional solution.

Conclusion

The dimensions and connections of taps are an area where the "boring technical side" directly affects whether the installation takes an hour or a whole day with two visits to the store. The imperial threads G 1/2" and G 3/4" are not arbitrary – they are the result of a system established over decades, which has its own logic. The center distance is not just a number on paper – it is the physical reality of your bathroom, which you can measure today so that you can shop with confidence tomorrow.

If you want to take the topic further, also check out other articles in our Knowledge Center: How to choose water taps for your bathroom and kitchen will cover selection by room type, Replacing the gasket and cartridge in a tap: when and how to do it will help with maintenance, and How to maintain and clean taps without damaging the surface will extend the lifespan of your new tap to the maximum.

Find the full range of water taps in the category Water taps – with filtering by type, size and surface finish.

Do you have a question about this topic?

Can't decide or are you dealing with a specific situation at home? Write to us – we're happy to help.