What connection diameter and spacing do you need for a bathroom faucet

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What diameter and spacing of connections do you need for a bathroom faucet

When a customer chooses a new bathroom faucet – whether for a sink, bathtub or shower – they are usually most interested in the design, surface finish and price. Only when it comes to the actual replacement do they find out that the faucet they bought simply does not "fit" the existing plumbing. Either it has a different thread diameter or the spacing of the connecting hoses does not match the distance of the connections in the wall or in the sink. Result? Another trip to the store, unplanned costs for a plumber or, in the worst case, returning the product.

This article was created precisely to help you avoid this situation. We will explain in detail what terms such as G 1/2", spacing 150 mm, eccentric or connection kit mean, why these parameters are just as important as the appearance of the faucet when choosing it, and how to measure them correctly before you order a new faucet.

What is a "faucet connection" and why it matters

Every water faucet connects to the water supply through threaded connections. These connections have a precisely defined thread diameter and – in the case of two-outlet (two-connection) faucets – also a mutual distance, i.e. spacing. These two dimensions are absolutely key to the compatibility of the new faucet with the existing installation.

In practice, every second customer who changes the faucet themselves asks about this. And while we're at it – if you're interested in the complete step-by-step process of replacement including tools and difficulties you might encounter, see the article Installation of Stern water faucet step by step – DIY or with a plumber in this Knowledge Center. Here we will focus exclusively on the dimensional parameters of the connection.

Thread diameter: G 1/2" as the golden standard

Almost all bathroom faucets available on the European market – including the entire range of Stern water faucets – use a thread according to the BSP (British Standard Pipe) standard marked as G 1/2". It is an external (male) thread on the hoses or connection kit of the faucet, which is screwed into the internal (female) thread in the corner valves or direct valves of your installation.

What exactly does "G 1/2"" mean?

The letter G denotes the type of thread – cylindrical (cylindrical) pipe thread according to ISO 228. The number 1/2" is the nominal bore, not the actual external diameter of the thread. This confuses many people: the actual external diameter of the G 1/2" thread is approximately 20.955 mm (i.e. almost 21 mm), not 12.7 mm (half an inch). The thread has 14 threads per inch (14 TPI).

For practical purposes, it is enough to know: if you have corner valves with an internal G 1/2" thread in your bathroom (which is almost all apartments and houses today), you will be able to connect to any standard faucet with an external G 1/2" thread without any problems.

Exceptions and less common diameters

There are cases when you will encounter a different diameter:

G 3/8" – occurs in some older installations or certain types of sink faucets for shallow cabinets. The external diameter of the thread is about 16.7 mm.
G 3/4" – used in bathtub faucets with side flow (thicker supply), less common in ordinary households.
M10 × 1 – a special metric thread that appears on some sink faucets with very thin tubes (e.g. for designer toilet sinks with minimal space).
Old installation 3/4" BSP – in panel houses from the 50s–70s you may encounter thicker steel pipes, where a reducing piece is needed.

If you are not sure what you have at home, the simplest way is to unscrew the supply hoses from the corner valve and have the thread measured with a caliper, or take the old faucet (or hose) to the store and have it identified.

Center distance: 150 mm as the European standard

Center distance (in English "centre distance") is the distance between the axes of hot and cold water. We always refer to the center-to-center distance, i.e., from the center of one hole to the center of the other. This number is particularly important for two-outlet taps (basin, bathtub, shower).

The European standard, which is also valid on the Slovak market, sets the standard center distance at 150 mm. This value is binding for most apartment installations carried out from the 1980s until today. So, if you are replacing a tap in a panel apartment or in a new building, it is most likely that your center distance is exactly 150 mm.

What if the center distance does not match? Eccentrics as a solution

In practice, it often happens that the measured center distance differs from 150 mm – and this can be in both directions. There are several reasons for this:

Old installations carried out according to different standards (e.g., 130 mm, 180 mm)
Inaccurate placement of outlets during reconstruction or do-it-yourself installation
Combination of different pipes and fittings, where the center distance has changed compared to the original design
Imported taps with a different national standard (e.g., some Italian or Spanish taps from another period)

The solution is eccentrics (also called eccentric adapters or eccentric couplings). These are threaded intermediate pieces with an external G 1/2" thread, whose outlet axis is shifted by several millimeters relative to the inlet axis. Most eccentric couplings allow compensation in the range of ±10 to ±15 mm – which means they can "cover" a center distance of roughly 120 to 180 mm.

Eccentrics are commonly supplied with wall-mounted bathtub and shower taps, as the risk of inaccurate outlet placement is much higher with these than with basin taps (where the center distance is determined by the hole in the basin itself).

Basin taps: center distance determined by the basin

The situation is a bit different with basin taps. The tap is mounted directly into the hole in the basin, not into the wall. Therefore, the center distance of the outlets in the wall (or in the floor in the case of a stand-up tap) is not limiting – flexible connecting hoses can adapt to various distances.

The limiting factors here are primarily:

Diameter of the mounting hole in the basin – standard 35 mm for regular taps, but it can also be 52 mm or another size in design basins
Wall thickness (slab) of the basin – affects the length of the fixing screw of the tap
Number of holes – single-hole basins accept only single-lever or thermostatic taps, three-hole basins (center + two sides) are for the older type of two-outlet taps

The supply hoses (flexible hoses) of the basin tap are usually 300 to 500 mm long and have a G 1/2" thread at the end – this is connected directly to the angle valve. The flexibility of the hoses solves practically any spatial differences between the axis of the tap and the axis of the angle valves.

More about types and use of basin taps can be found in the article Basin vs. Shower vs. Bathtub Taps Stern – Differences and Use in this Knowledge Center.

Bathtub and shower taps: center distance and depth matter even more

With bathtub and shower taps, the situation is more complicated, as these taps are mostly mounted on the wall (wall console) and the outlet connections are embedded in the plaster. Here, it not only depends on the center distance, but also on the depth of the connection (so-called embedding depth).

Standard center distance 150 mm for bathtub taps

For bathtub taps with side outlets (the tap is mounted on the wall next to the tub), the same 150 mm standard applies. The connections are in the wall, and the tap is screwed to them via eccentrics or directly via a G 1/2" thread.

The embedding depth of the connection should be in the range of 20–25 mm below the finished wall (with tiling). If the connections are embedded too deep (e.g., 40–50 mm), standard eccentrics will not help and you will need extension pieces. On the other hand, if the connections protrude too much, they need to be shortened or shorter eccentrics used.

Shower taps and thermostatic taps

Shower taps, including thermostats, also have a center distance of 150 mm, but with premium thermostatic sets, you may occasionally encounter a center distance of 180 mm – especially in horizontal arrangements (temperature control on the left, volume on the right, output switch in the center). Always read the technical specifications of the specific model carefully.

For taps with underfloor installation (underfloor taps), completely different rules apply – here it mainly depends on the type and size of the underfloor body, which is embedded in the wall during the rough build, and the external valve (control + shower) is connected to it via a specific manufacturer adapter. These systems are not interchangeable between manufacturers.

How to correctly measure the center distance before buying a tap

This is the number one question with every tap replacement. Here is the procedure:

Step 1: Turn off the water

Before any manipulation, close the angle valves (or the main shut-off valve, if you don't have angle valves). Turn the tap and let the remaining water drain from the pipes.

Step 2: Remove the old tap or hoses

Loosen the connecting hoses from the angle valves. If the original tap is dry-mounted into the wall (bathtub, shower), unscrew the eccentrics from the wall.

Step 3: Measure the Spacing

Using a sliding caliper or a ruler, measure the distance between the centers of both holes (threads) in the wall. The center of the thread is the axis of the hole — that is, the center of the circle you see when you look directly into the hole. If you have an eccentric or corner valve in the wall, measure the distance between the centers of the outlet threads.

Step 4: Check the Thread Diameter

The outside diameter of the corner valve thread should be G 1/2" — if you measure the outside diameter of the thread with a sliding caliper and get a value around 20–21 mm, it is G 1/2". If you get approximately 16–17 mm, it is G 3/8".

Step 5: Check the Embedment Depth (Only for Wall-Mounted Taps)

For your bath and shower taps mounted on the wall, measure by how many millimeters the thread is aligned or recessed below the surface of the wall (with tiling). This number is needed to correctly select eccentrics or extension pieces.

Tap Connection Kit: What's in the Package and What You Need to Buy Separately

Most bathroom taps in the category of Stern water taps are delivered with a so-called connection kit in the package, which includes:

Two flexible hoses – usually 300 mm or 400 mm in length, with sealing, thread G 1/2"
Fixing nut and rubber seal (for basin taps)
Trap (for some basin series)
Handle / lever + cover (depends on the type)

What is not part of the package and needs to be obtained separately:

Corner (shut-off) valves – if you don't have them or they are old and leaking
Sealing between the corner valve and the hose – sometimes it is part of the hose, but not always
Eccentrics – for bath/shower taps, if the manufacturer does not include them
Shower hose, handheld shower, and shower arm – for shower sets, depending on the specific model
Trap set for a bath tap with an outlet into the bath

Always check what a specific model's package includes and what you need to add before ordering. It will save you an unnecessary trip to the store on the installation day.

Special Situations: When Standard Dimensions Are Not Enough

Old installation with steel pipes – spacing 130 mm

In apartment buildings built in the 1950s to 1970s, we sometimes encounter a spacing of 130 mm or even 120 mm. These installations were made from galvanized steel pipes and mounted according to the standards of that time. If you are replacing a bath tap in such a building, you have two options:

Use eccentrics that can compensate for the difference from 150 mm to 130 mm (most standard eccentrics can handle this).
Have the piping system modified (a more expensive but long-term clean solution, especially if the old pipes are in poor condition).

New construction with non-standard spacing

Paradoxically, even in new constructions, it can happen that the plumber installed the connections with a deviation of 10–20 mm from the planned position during the rough installation. The reasons are often different tile thickness than expected, or a changed position of the bath compared to the project. In such cases, always check the position of the connections before tiling and adjust them if necessary, while the wall is still open. After tiling, any correction is much more expensive.

Design basins with atypical holes

Some modern basins – especially design stone basins, concrete cast basins, or thin ceramic basins – have a mounting hole of a different diameter or non-standard thickness. In such cases, always check before buying the tap whether the manufacturer or seller of the basin recommends a specific type of tap or at least specific dimensions (hole diameter, maximum/minimum wall thickness, type of fixing).

Water pressure and spacing – an apparent inconsistency that actually connects

You might be surprised to learn that spacing and the diameter of the connection are, to some extent, related to the water pressure in your installation – not directly, but through the choice of hoses. If you have higher water pressure (over 4 bar), it is advisable to use braided stainless steel flexible hoses (so-called "armored") that are more resistant to bursting. Their length and end threads (G 1/2") are the same, but the construction is more robust. This parameter is important especially in apartments with a direct connection to the public water supply without a pressure-reducing valve.

For more information on water pressure and its impact on taps, read the article Common Questions About Stern Taps – Water Pressure, Compatibility, Warranty, and Service in this Knowledge Center.

Summary: Table of the Most Important Dimensional Parameters

Parameter	Standard Value	Possible Deviations	Solution in Case of Deviation
Thread Diameter	G 1/2" (≈ 21 mm)	G 3/8", G 3/4"	Thread reduction
Spacing of Connections	150 mm	120–180 mm	Eccentrics (eccentric pieces)
Mounting Hole (Basin)	35 mm	26 mm, 52 mm	Correct tap for the hole
Embedment Depth (Wall)	20–25 mm	0–50 mm	Other eccentrics / extension
Length of Flexible Hoses	300–500 mm	200–600 mm	Longer hose
Outlet Thread (Bath, Shower)	G 1/2" or G 3/4"	Depends on the model	Correct hose or connector

Practical experiences from regular orders

In practice, when replacing a bathroom faucet, we repeatedly encounter several similar situations. Allow us to share the most common ones so you can avoid them:

Situation 1: The customer has an old panel bath in the bathroom and is replacing the bath faucet. The distance is measured and it comes out to 150 mm – great, standard. The problem, however, arises with the depth of installation: old plumbers embedded the connections too deep (about 40 mm behind the tiling), because they expected a thicker plaster layer. Solution: longer eccentric fittings or special G 1/2" extension sleeves.

Situation 2: The customer replaced the sink with a modern, shallow "flat" sink. The new sink has a mounting hole of only 26 mm (the original faucet on the old sink had a 35 mm hole). The faucet the customer chose simply does not fit through the smaller hole. Solution: buy a faucet designed for a 26 mm hole, or check whether the hole can be enlarged (not always possible with ceramic).

Situation 3: Bathroom renovation, new shower set. The customer embedded the connections himself before tiling, but deviated by 15 mm from the axis – one connection is 75 mm from the center, the other is 90 mm (total distance 165 mm instead of 150 mm). Solution: eccentric fittings will help, but only if the distance does not exceed 180 mm. Lesson: always use a template or at least a ruler before embedding the connections in the wall.

Situation 4: The customer bought a faucet from an international e-shop, the thread diameter is 3/8". The angle valves in his bathroom are standard G 1/2". Solution: reduction from G 1/2" to G 3/8" – simple and cheap, but the customer did not know about it and returned the product. Lesson: always check the thread of the angle valves and compare it with the faucet's technical specifications.

How to choose the right faucet – checklist before ordering

Before you click "Add to cart," ask yourself these questions:

✔ What is the thread diameter of your angle valves? (G 1/2" – standard)
✔ What is the distance between your connections? (150 mm – standard; if not, do you have eccentric fittings?)
✔ What is the diameter of the mounting hole in your sink? (35 mm – standard)
✔ How many holes does your sink have? (1 hole = single-lever; 3 holes = double-tap type)
✔ What is the depth of the embedded connections behind the wall? (20–25 mm is ideal)
✔ Does the package include a flexible hose, seals, and a fixing nut?
✔ Do you need to buy angle valves, eccentric fittings, a trap, or shower accessories separately?

If you are unsure of the answer to any of these questions, it is better to consult before ordering – you will save time, money, and nerves. For more information on what to focus on when choosing, see the article How to choose Stern water faucets – what to focus on before purchase in this Knowledge Center.

Frequently asked questions (FAQ)

Do I need to measure the distance when replacing a faucet with the same type?

If you are replacing a faucet with the same model or type (for example, a single-lever sink faucet with another single-lever one with flexible hoses), you usually do not need to measure the distance – the flexible hoses will adapt. However, we recommend measuring it for a bath or wall-mounted shower faucet, because the eccentric fittings of the old faucet may not match the new one. If you accidentally order an unsuitable one, you will have to wait for delivery and unnecessary problems will arise.

Can I connect an old G 3/8" angle valve to a new faucet with G 1/2"?

Not directly – the threads are different and must not be forced. The solution is a reduction from G 1/2" male to G 3/8" male (or female, depending on the configuration of your angle valve). These reductions are cheap and available in every hardware store. Despite this, we recommend replacing the old angle valve with a new G 1/2" one – you will have a compatible and reliable connection for many years.

What are eccentric fittings and where can I buy them?

Eccentric fittings (eccentrics) are connecting spacers that allow compensation for the difference between the actual distance of the connections in the wall and the standard distance of the faucet (150 mm). They look like short metal rods with an external G 1/2" thread on one end and an internal G 1/2" thread on the other, with the axes of the input and output threads offset. They are usually sold in pairs and are available in hardware stores and sanitary shops. Always check the range of compensation the eccentric fittings allow before purchasing (usually ±10–15 mm).

Why is my bath faucet leaking, even though I tightened it properly?

There may be several reasons, but the most common is a missing or damaged seal between the eccentric fitting and the wall, or between the eccentric fitting and the faucet. Another possible cause is insufficient sealing of the thread (inadequately or insufficiently wrapped Teflon tape). Also check whether the faucet is parallel to the wall and whether you tightened the eccentric fittings flush (not just snug). For more information on leaks, see the article Dripping or leaking Stern faucet – causes and repair in this Knowledge Center.

Can I use longer flexible hoses if the original ones are not long enough?

Yes, G 1/2" flexible hoses are available in various lengths from about 200 mm up to 600 mm (and even longer). It is important to maintain the correct thread diameter on both ends (G 1/2") and to use hoses certified for potable water. With longer hoses, make sure they are not kinked or twisted – this would restrict the flow and damage the seal.

How can I check whether my angle valves are in good condition before I start replacing the faucet?

Close the angle valve and observe whether it actually stops the water flow. If the faucet still drips after the valve is closed, the valve is leaking and we recommend replacing it together with the faucet – this will save you one intervention in the installation. Worn angle valves can also be recognized by the fact that they are hard to turn or that the key turns, but the water still flows. Replacing an angle valve requires stopping the water supply at the apartment or house shut-off valve.

Conclusion: Measuring before purchase will save you time and money

The thread diameter and connection distance are two numbers that determine whether your new bathroom faucet will be easily installed or whether you will spend the weekend solving compatibility problems. In the vast majority of Slovak households, the standard applies: G 1/2" and a distance of 150 mm. If these values are confirmed by measuring your installation, you can choose practically any faucet from the Stern water faucet range without worrying about incompatibility.

If your measured values deviate, do not panic – there are solutions (eccentric fittings, reductions, longer hoses) that will save the situation without interfering with the installation. The important thing is to know about them in advance and not discover them only during the actual installation.

Choosing the right faucet is not just about how it looks. It is about whether the faucet you order will actually fit into your bathroom – on the first try, without surprises. And that is exactly what we want to help you achieve with this article.

Do you have a question about this topic?

Having trouble deciding or dealing with a specific situation in your home? Write to us – we are happy to help.