How to Choose a Pipe Connector or Fitting

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How to Choose a Pipe Connector or Fitting for a Heating or Water System

When planning or repairing a heating or water system, attention almost always focuses on the pipe, the radiators, the boiler or the tap - fittings and connectors seem like a minor detail that we only remember once a joint starts to drip, or once we realize at the shop that we bought the wrong part. In reality, it is exactly the opposite: without the right fitting, it is simply not possible to connect the pipe to a radiator, a tap, a manifold, or to route it around a corner of the room. A fitting is therefore just as important a part of the system as the pipe itself, and choosing or installing it incorrectly is one of the most common causes of leaks that only appear after months or years of operation.

In this article we will explain, in practical terms, what a fitting (connector) actually is and what it is used for, what the difference is between a screw joint and a press joint, what types of fittings exist and when each is used, why the material matters (brass vs. plastic), how to check that a fitting is compatible with a specific pipe, what tools you will need for installation, and which mistakes to avoid so that the joint lasts for decades without a drop of water on the floor. The article also includes real products with prices and links, two practical examples, and answers to the questions we are asked most often on this topic.

The article is intended equally for a beginner DIYer replacing a bathroom tap on their own, and for an installation company that needs to quickly check whether a specific fitting fits a given type of pipe. If you are planning a larger renovation of your pipework, we also recommend reading the related topics we link to throughout the text.

What a fitting is and why it matters so much in a pipe system

A fitting (commonly also called a connector) is a component designed for joining, branching, reducing the diameter of, or changing the direction of a pipe system. It is a collective term for a whole group of small but functionally key components - from a simple straight connector, through an elbow and a T-piece, all the way to a wall plate used to anchor the pipe at the point where a tap is connected. Without the right fitting it would not be possible to connect the pipe to a radiator, a tap, a manifold, or to route it around a corner of the room - fittings are therefore just as important a part of the system as the pipe itself.

In practice this means that even the highest-quality pipe loses its purpose if the fitting at its end does not match the required diameter, material and joint type. While pipe is usually bought in bulk by the metre, fittings are chosen one piece at a time for a specific point in the system - which is why it is important to know what types exist and when each one is used. That is exactly what the following sections of this article cover.

It is also worth remembering that a fitting is not just a mechanical joining piece, but also a potential point of failure. Material quality, manufacturing precision and, above all, correct installation determine whether a joint lasts for decades or becomes the weak point of the whole system after just a few seasons.

Screw vs. press fittings - which joint type to choose

When choosing a fitting, the first and most important decision is the joint type - that is, the way the fitting is joined to the pipe. In practice you will most often encounter two variants: a screw (compression) joint and a press joint. Both have their advantages and limitations, and the choice between them affects not only the cost of installation, but also which tools you will need and whether the joint can easily be taken apart again in the future.

A screw joint is secured with a union nut that presses a sealing or retaining ring against the pipe. The advantage of this solution is that it can be taken apart without special tools - a pair of pliers or a suitable wrench is enough. This is especially practical for maintenance, or whenever a joint needs to be adjusted later, for example when replacing a tap or reworking part of the system. Screw fittings are therefore a popular choice for smaller repairs, DIY installation, and anywhere future intervention is expected (for example, connecting a tap through a wall plate).

A press joint, by contrast, is created using press pliers that permanently deform a metal sleeve around the pipe inserted into the fitting. Installation is faster when many joints need to be made at once, and the resulting joint is stronger and non-detachable, which is an advantage for extensive pipework in new builds or complete renovations. The downside is the need to invest in press tools compatible with the given system - and since different manufacturers may use a different press jaw profile, tools and fittings from different brands cannot simply be combined.

When deciding, consider above all the scope of the work and whether you already own press tools (or whether it is worth buying them). For a one-off repair or replacing a single section of pipe, a screw joint is usually the more advantageous option, while for a larger system renovation a press system will save time and effort. You will find a more detailed comparison of both systems in the separate article Screw vs. Press Joints.

Screw Fitting 1/2x16 with Female Thread

A screw transition fitting with a 1/2" female thread, designed for pipe with a 16 mm diameter. A typical example of a fitting that can be installed without press tools - a suitable wrench and pliers are enough.

Price: 1.72 €

Types of fittings - elbow, T-piece, reducer and wall plate

The four most common types of fittings and their role in a pipe system.

Besides the joint type, the second important decision is the shape and function of the fitting - in other words, what role it needs to play at a specific point in the system. In practice you will most often come across four basic types.

A straight connector joins two sections of pipe of the same diameter in a single line - it is used wherever you need to extend a run or replace a damaged section of pipe without changing direction or diameter.

An elbow changes the direction of the pipe, most often by 90° or 45°. Elbows are essential anywhere the pipework needs to go around a corner of the room, drop down to the floor, or, conversely, rise up to the ceiling. Without an elbow, the pipe would have to be bent mechanically, which for many materials (for example copper or PP-R) is either difficult or simply not recommended.

A T-piece branches a single run into two directions. It is used, for example, to branch off to a radiator from the main riser pipe - in other words, whenever you need to "branch off" from one pipe to another appliance without interrupting the original run.

A reducer (transition piece) joins two sections of pipe of different diameters. It is typically used when transitioning from a thicker main line to a thinner pipe running to an individual radiator or appliance, or conversely when connecting a smaller pipe to a larger profile.

A wall plate is a special fitting designed to firmly anchor the pipe into the wall at the point where a tap or other appliance is connected to it. It must be anchored extra securely, since it carries the mechanical load from tightening and using the tap - that is, repeated tightening of the hose, and possibly rough handling during everyday use. A wall plate is therefore one of the few fittings where it is worth investing in a higher-quality version even when the rest of the system is done more cheaply.

Screw Wall Plate 1/2 x 16 for Water

A screw wall plate for firmly anchoring a tap into the wall, with no need for press tools, for pipe with a 16 mm diameter. Thanks to its screw design it can easily be taken apart if needed (for example, when replacing the tap).

Price: 2.83 €

A detailed overview of all fitting types, including recommendations on when to use each one, can be found in the separate article Types of Fittings – Elbows, T-pieces, Reducers, Wall Plates. If you are dealing with a specific tap connection, we also recommend the article Wall Plates for Taps – What They Are and How They Are Installed.

Brass vs. plastic - which material to choose for a fitting

Besides the joint type and the shape of the fitting, the third key parameter is the material the fitting is made from. On the market you will commonly come across two main categories - brass and plastic (for example PPSU or POM) - and the choice between them directly affects what type of system the fitting is suitable for.

Brass fittings are resistant to both temperature and pressure, suitable for heating and hot-water systems, and remain stable over the long term. Their disadvantage is a higher price and greater weight compared with plastic alternatives. This is exactly why brass fittings are the first choice wherever the system carries hot water or a heating medium under higher pressure - typically when connecting radiators, manifolds or a boiler.

Plastic fittings (for example made of PPSU or POM) are lighter and cheaper, resistant to corrosion, but have a lower maximum operating temperature and pressure than brass. They are therefore better suited to cold-water systems or applications with lower operating temperatures. Before using a plastic fitting on a heating circuit, always check the technical data sheet of the specific product - parameters vary between products, and not every plastic fitting is rated for the temperatures common in a heating system.

Put simply: if you are not sure which material to choose, for a heating system it is better to go with brass - the higher purchase price pays for itself through a longer service life and a lower risk of leaks during temperature fluctuations. Save plastic for systems that do not involve high temperature or pressure. You can find more on this topic in the article Brass vs. Plastic Fittings.

Fitting compatibility with pipe - what to watch out for

One of the most common mistakes when buying a fitting is assuming that a fitting of the same "nominal" diameter automatically fits any pipe. In reality, the fitting must match the exact outer or inner diameter of the specific pipe and the joining method it is designed for. A fitting designed for a screw joint on 16 mm PEX-AL-PEX pipe is not automatically compatible with copper or PP-R pipe of the same nominal diameter, since the actual dimensions and joining method differ between materials.

When buying a fitting, it is therefore always necessary to check that the material, diameter and joint type match the pipe already installed in the system. We recommend proceeding in three steps:

1. Find out the exact material and diameter of the existing pipe (for example PEX-AL-PEX 16 mm, copper 15 mm, PP-R 20 mm).
2. Check that the fitting is designed specifically for that material and diameter - not just for a "similar" or "roughly the same" size.
3. Check that the fitting's joint type (screw or press) matches the tools you have available, or are willing to buy.

In practice, incorrectly judging compatibility is one of the most common reasons a fitting has to be returned or replaced after purchase - and, in the worse case, why a leak only appears after an entire section of the system has been assembled. Never leave checking compatibility to "eyeballing it".

Reducer Socket 1" x 1/2" FF

A brass reducer socket with 1" and 1/2" threads (FF = female/female thread). A typical example of a reducer that allows a transition between two different pipe diameters without having to replace the whole section of pipe.

Price: 4.18 €

Approximate prices of the three fittings mentioned in this article.

A detailed guide on how to check, step by step, whether a fitting is compatible with a specific type of pipe can be found in the article Fitting Compatibility with Different Pipe Types.

Installing fittings - procedure and required tools

The tools needed for installation differ depending on whether it is a screw joint or a press joint. To install screw fittings, a set of suitable wrenches (or an adjustable wrench) is generally enough, along with a pipe cutter to keep the pipe end straight and square - a straight cut is, after all, the basic precondition for the sealing ring to seat correctly and prevent leaks.

For press joints, on the other hand, press tools compatible with the given fitting system are essential. Since different manufacturers may use a different press jaw profile, using the wrong pressing profile can result in a leaking or damaged joint even though the operation appears to have been carried out correctly - in other words, even if the joint looks flawless at first glance, it may be technically under-pressed. Before buying press tools, therefore, always check that they are designed specifically for the fitting system you plan to use.

Basic steps for installing a screw joint, based on the procedure in this article.

In simplified terms, the basic procedure for installing a screw joint looks like this: the pipe is trimmed to a straight, square end, the union nut and the sealing/retaining ring are then slid onto the pipe, the pipe is pushed fully into the fitting body, and the nut is tightened with a suitable wrench - but not with excessive force, which could damage the thread or the sealing ring. For a press joint, the pipe is pushed fully into the fitting (it is important to check that it is inserted correctly, ideally up to the marking, if the fitting has one), and the sleeve is then pressed with suitable press pliers in a single smooth motion.

A complete installation procedure, including the recommended order of steps and a list of the tools you will need, can be found in the separate article Installing Fittings – Procedure and Required Tools.

Common installation mistakes and how to avoid them

Most leaks at fittings do not happen because the fitting is faulty, but because the installation was not done carefully. The most common mistakes include:

An insufficiently tightened union nut on screw joints - the most common cause of leaks. The nut must be tightened so that the sealing or retaining ring is pressed evenly all around the pipe, but without excessive force.

A damaged or missing sealing ring - often caused by careless handling during installation, or by reusing an old, already worn ring when a joint is taken apart and put back together.

Pipe inserted at an angle or not far enough into the fitting before pressing - for a press joint this is a particularly risky mistake, since after pressing the fault can no longer easily be spotted visually without taking the joint apart.

Combining incompatible materials, for example brass directly with aluminium without proper separation, in a damp environment. Over time this can cause electrochemical (bimetallic) corrosion at the joint - a slow but ongoing process of metal damage that only becomes visible after a longer time, by which point the repair is more complicated.

The common thread in all these mistakes is a lack of care during preparation and installation - which is why it is worth giving every joint the same attention, even if it is "just" a small fitting. A detailed overview of mistakes and recommendations on how to prevent them can be found in the article Common Installation Mistakes and Leaks. If a leak has already appeared and you need to repair it or replace the fitting, the article Servicing and Replacing Fittings can also help.

How to decide - a summary of the selection process

Four questions that will help you choose the right fitting.

If you are not sure which fitting you need, it is worth going through a simple sequence of questions:

1. What function does the fitting need to perform at that point? A straight connector extends a straight run, an elbow changes direction, a T-piece creates a branch, a reducer changes the diameter, and a wall plate anchors the pipe to the wall before connecting an appliance.
2. What type and diameter of pipe is already installed in the system? The fitting must match the material and diameter of the existing pipe - not just a "similar" size.
3. Which joint type do you prefer? A screw joint for a one-off repair or wherever you expect to take the joint apart in the future, a press joint for a larger installation where you have suitable press tools available.
4. What fitting material should you choose? Brass for heating systems and hot-water systems, plastic (after checking the technical data sheet) for cold-water systems or lower operating temperatures.

If, after going through this sequence, you are still not sure, feel free to contact us using the form at the end of this article - we are happy to advise based on your specific situation at home or on site.

Real-life examples

Example 1: A family house with a bathroom tap replacement
In an older family house, the original bathroom tap was connected directly to a copper pipe with no wall plate - the pipe was only slightly bent, and the tap rested directly against the wall with no firm anchoring. With everyday use (tightening the hose, cleaning around the tap), the joint gradually loosened until a slight leak appeared at the base of the tap. The solution was to install a screw wall plate of the right diameter directly into the wall, to which the tap could be firmly anchored. Thanks to the screw design of the wall plate, the whole job could be done without press tools, using only standard wrenches, while still leaving the option to easily take the wall plate apart again in the future if the tap ever needs replacing.

Example 2: A panel-building flat with a branch to a radiator
In a flat in a panel building, during a bathroom renovation it was necessary to branch off from the main riser pipe to a newly positioned radiator, which was being moved to a different spot on the wall than the original one. Since the main riser pipe had a larger diameter than the run leading to the radiator itself, it was necessary to use a combination of a T-piece (for the branch itself) and a reducer (for the transition to the smaller pipe diameter leading to the radiator). When choosing the fittings, the material compatibility with the existing pipework was carefully checked, since part of the original pipe was copper and the new branch was to be done in PEX-AL-PEX - using an incompatible transition here could have led to a risk of electrochemical corrosion at the point of contact between the two metals. In the end, a suitable transition fitting with a brass body was chosen, which safely separated both sides of the system while still ensuring sufficient tightness at the operating temperature of the heating water.

Frequently Asked Questions About Connectors and Fittings (FAQ)

1. What is the difference between a fitting and a connector?
In everyday practice, both terms are used as synonyms - a "connector" is just one specific type of fitting (a straight connector), while "fitting" is the general term for the whole group of components used for joining, branching, reducing the diameter of, or changing the direction of a pipe system.

2. Can I replace a screw fitting with a press fitting on the same pipe at any time?
Not automatically - it depends on whether the pipe and its end are prepared for that joint type. When switching from a screw to a press system, it is usually also necessary to adjust the end of the pipe, or possibly replace a longer section of the system.

3. Is a brass fitting always a better choice than a plastic one?
For heating systems and hot-water systems, yes, since brass better withstands higher temperature and pressure. For cold-water systems, a plastic fitting may be sufficient and more advantageous in terms of both price and weight - but always check the technical data sheet of the specific product.

4. Why does my joint drip even though I tightened the nut properly?
The most common cause is a damaged or missing sealing ring, or the pipe having been inserted into the fitting at an angle. Also check that the end of the pipe is straight and square - an uneven cut prevents the seal from seating correctly.

5. Do I need special tools for screw fittings?
No, a set of suitable wrenches (or an adjustable wrench) is generally enough, along with a pipe cutter to trim the end if needed. This is one of the main advantages of a screw system over a press system.

6. Why is the wall plate at a tap so important?
A wall plate firmly anchors the pipe into the wall exactly at the point where the tap connects to it. It must be anchored extra securely, since it carries the mechanical load from tightening and everyday use of the tap - without it, the joint would be exposed to unnecessary stress and could loosen or become damaged over time.

7. Can I combine fittings from different manufacturers in a press system?
This is not recommended. Different manufacturers may use a different press jaw profile, and using the wrong pressing profile can result in a leaking or damaged joint even though the operation appears to have been carried out correctly.

8. How do I know whether a fitting fits my pipe?
Check the material and exact diameter of the existing pipe and the joining method (screw or press), and compare it with the technical parameters of the fitting. A fitting designed, for example, for 16 mm PEX-AL-PEX pipe may not automatically fit copper or PP-R pipe of the same nominal diameter.

Have a Question About Connectors or Fittings?

Not sure what to choose, or dealing with a specific situation at home? Write to us - we are happy to help.