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A Complete Guide to Using Plumbing Fittings for Joining PVC, PEX, and Copper Pipe

Updated on November 18, 2017
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Eugene, an avid self-taught DIYer, has acquired 30 years of experience with power/hand tools, plumbing, electrics, and woodwork.

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A DIY Guide to Plumbing

Basic plumbing isn't rocket science. If you are reasonably adept at DIY, learn some of the basics, and take care when putting everything together, it's not too difficult. This is a basic guide to pipe types, plumbing fittings, thread sizes, and how to use fittings to connect copper, PVC, and PEX pipes.

What Materials Are Used for Plumbing Pipe?

Plumbing pipe is made from various materials, copper, galvanized steel and iron, polyvinylchloride (PVC), chlorinated polyvinylchloride (CPVC), cross-linked high density polyethylene (PEX), and polybutylene. Fittings are made from brass, plastic, copper, or malleable iron.

  • Copper This is widely used and can withstand very high temperatures. It is exclusively used for the final connections made to central heating boilers/furnaces where temperatures may exceed 100 C (212 F). The disadvantage of copper pipe (or "tube" as it is known in the plumbing industry) is that it is rigid and either must be bent into shape using special tools, or alternatively by using discrete lengths of pipe and 45 or 90 joints.
  • Stainless Steel In the 70s, stainless steel plumbing was popular when there was a copper shortage. It is even more rigid than copper so slight alteration by bending can be difficult. Stainless steel is supposed to be more corrosion resistant than copper and is sometimes used for aesthetic reasons where plumbing must be exposed.
  • PVC and CPVC Piping made from these polymers (plastic) has several advantages over copper. Plastic pipe is ductile and can be easily bent, lessening the need for bends. If a really tight bend is required, 90 degree elbow joints can be used. It can also be easily routed through floor and wall spaces. Plastic is a better insulator than metal, so heat loss is reduced. Usually plastic piping has more "give" and will stretch more than copper when water freezes and expands inside the pipe, reducing the danger of bursting in sub-zero temperatures.
    PVC or poly vinyl chloride is the most basic type of plastic pipe use for both drinking water plumbing and waste pipe. Chlorinated PVC or CPVC has the same characteristics as standard PVC but has better corrosion resistance at higher water temperatures and is also significantly more ductile.
  • PEX Plumbing tubing is also made from cross-linked high-density polyethylene or PEX. This is a tough ductile material which can survive temperatures as low as -20 C (-4 F) without bursting. PEX is also less than half the price of copper and doesn't corrode when used in areas where the water supply is acidic. Just like PVC, PEX is flexible and can be bent over a tight radius and easily routed to fittings. It does expand more than copper, so shouldn't be stretched to reach fittings and allowed to drop slightly between fixings to allow for contraction. On long runs, a loop of tubing can be included in a line to allow for a lot of contraction. When running tubing through holes in walls, make the holes sufficiently large so that tube can slide freely as it expands and contracts. PEX is susceptible to UV and if used outdoors, it needs to be shielded using insulation or otherwise to prevent degradation.
  • Ductile (Malleable) iron Used for water, gas, compressed air, and as a rigid metal conduit (RMC) for housing cables in industrial and commercial applications. It is much stronger than copper or plastic pipe but not so common in domestic installations. Ductile iron or cast iron was often used for larger diameter water mains before the advent of plastic.
  • Lead No longer used for plumbing in new installations because of concerns over toxicity of the metal, lead piping was phased out after WWII when copper became popular.

Care needs to be taken when working near plastic piping or fittings to avoid heat damage from blow torches or other heat producing tools. Piping should also be routed during installation so that it isn't subjected to high temperatures from heat sources such as flues.

1/2 inch PEX pipe can be bent  to a min radius of 4 inches (depending on wall thickness)
1/2 inch PEX pipe can be bent to a min radius of 4 inches (depending on wall thickness) | Source
3/4 inch BSP ductile iron pipe and coupler
3/4 inch BSP ductile iron pipe and coupler | Source

Types of Plumbing Fittings

Fittings are made from various materials including plastic, brass, copper and iron. There are a huge variety of types with different functions including, 90 and 45 degree elbows, offsets, T-joints, Y-joints, cross joints, gate valves, ball valves, non-return (check valves), reduction fittings, couplers and flange (bulkhead) fittings for making a connection to oil or water tanks.

  • Brass threaded and compression fittings These have 2 or more ports or entry points for connection to pipes or fixtures. They may be compression only, compression and screwed, or screwed only. The compression port is used for connecting a pipe and the screwed port (if included), known as a union, connects to a fixture or device such as a radiator, WC, furnace, spiggot, pressure gage, water tank etc. The screwed section of the fitting may have male or female threads. Fittings with compression ports only, are used to join 2 or more pipes together, and are simple to use by the average DIYer once pipes are prepared correctly, and the fitting is assembled properly. This type of fitting makes use of a copper or brass olive ring also known as a ferrule, which is slid onto the end of the pipe before insertion. This is then deformed and squeezed tightly against the tapered surface of the fitting as a nut on the pipe is tightened. This seals the fitting and prevents water leaking out.
    Compression fittings can be used for connecting plastic or copper pipe and although easy to use, are relatively bulky and more expensive than other methods used for making joints. Another disadvantage is that a pipe can possibly turn within the fitting (e.g a coiled copper pipe behind an ice making refrigerator can turn as the fridge is pushed in and out repeatedly) , and over time this can cause leaks, so this needs to be taken into consideration. Compression fittings can be easily disassembled.
    Brass fittings are not recommended for use underground.
    Plumbers often use PTFE tape or jointing compound (which is like soft putty) on compression fittings to be totally sure they don't leak. However manufacturers don't recommend this because they reckon it can prevent the olive from sealing properly.
  • Capillary fittings are made from copper and employ a soldered joint to connect pipes together. The pipes to be joined are inserted into the fitting which is heated. Solder flows by capillary action to fill the small gap between pipe and fitting, sealing and making a strong joint which is resistant to pulling and rotation of the pipes. These type of fittings either come with a ring of solder included (Yorkshire fitting) or solder wire must be melted and fed into the joint as it is heated.
    Capillary fittings are slim and neat, inexpensive, and form a strong joint between pipes. However they are more difficult to use by the novice and since the fitting must be heated using a blowtorch, there is always the danger of fire when used in a confined space. Also preparation of pipes and fitting is essential, and these must be cleaned with wire wool so that solder flows and coats all the surfaces being joined.
  • Ductile (Malleable) Iron Screwed Fittings can be used with water and compressed air and are relatively inexpensive. These fittings are often encountered on the inlet/outlets of central heating boilers/furnaces, on pumps and on air compressors. Because iron is less expensive and stronger than brass, iron fittings are advantageous, especially when large sizes are required.
    Galvanized versions of these fittings are available which are resistant to external corrosion.
  • Plastic and Copper Alloy Push (Stab-In) Fittings are available for joining plastic and copper pipe. To use them, you just have to cut the end of a pipe square and push it into the fitting, which relies on an internal O-ring which compresses tightly against the pipe when inserted. These fittings also incorporate some form of collet / toothed ring arrangement which digs into the pipe and prevents it from being pulled out again.
    These type of fittings are very easy and convenient to use, especially in tight spaces, enabling pipes to be jointed quickly. They can also usually be disassembled by hand, or by using a special key. In both cases, this retracts the teeth, allowing the pipe to be removed. Fittings which can be disassembled by hand without using a key, sometimes have a twist lock feature. This gives added insurance, and locks the collet, preventing inadvertent release of a pipe from a fitting if something accidentally pushes against the collet. Sharkbite and Speedfit are two well known brands of these types of fittings

Push fittings can be used with copper, CPVC and PEX tube but aren't suitable for PVC. See Connecting PEX to PVC for more details.


For large projects, the cost of push or compression fittings on PEX can mount up. A cheaper alternative is crimp fittings which are slimmer but must be installed using special tools. See How to Install PEX Tubing - Making a Crimp Connection

Examples of Plumbing Fittings

Clockwise from top left: Compression elbow, iron reduction bushing with BSP threads, copper capillary elbow, compression elbow with 1/2 inch threaded BSP port,
Clockwise from top left: Compression elbow, iron reduction bushing with BSP threads, copper capillary elbow, compression elbow with 1/2 inch threaded BSP port, | Source
Speedfit, equal elbow, push fit (stab-in) plastic fitting. Speedfit is a registered trademark of John Guest Ltd
Speedfit, equal elbow, push fit (stab-in) plastic fitting. Speedfit is a registered trademark of John Guest Ltd | Source
Wall plate union and spigot, bib or outside tap. The wall plate union has 1/2 inch female BSP threads for connection to the spigot, and a compression input port for attaching to copper or plastic pipe
Wall plate union and spigot, bib or outside tap. The wall plate union has 1/2 inch female BSP threads for connection to the spigot, and a compression input port for attaching to copper or plastic pipe | Source
This 1/2 inch, malleable iron, 90 degree elbow, used on the output of an air compressor, has female BSP threads
This 1/2 inch, malleable iron, 90 degree elbow, used on the output of an air compressor, has female BSP threads

Sizes of Fittings, Pipe Sizes and Threads

Copper and plastic plumbing is technically referred to as tubing.
Steel plumbing is referred to as piping.

Pipe sizes and standards can be somewhat confusing. For example if you measure a 1/2 inch pipe or 1/2 inch fitting, neither the internal or external diameter of the pipe, nor the diameter of the thread are necessarily 1/2 inch. It is only called 1/2 inch for historical reasons. This dimension originally referred to the internal diameter of a pipe used with the 1/2 inch fitting, which in the early days of manufacture would have been thick walled.

  • U.S.A. - Fittings follow the National Pipe Thread Taper (NPT) standard defined in ANSI/ASME B1.20.1. Commonly used sizes are 3/8, 1/2, 3/4 and 1 inch. This dimension refers not to the diameter of the threads, but to the internal diameter of iron pipe used with the fittings (specifically Schedule 40 pipe). Copper and plastic tubing follows the Copper Tube Size (CTS) standard with outside diameter being 1/8 inch greater than the Nominal Pipe Size (NPS). For example a 1/2 inch tube has an OD of 1/2 + 1/8 = 5/8 inch
    Fittings can also have a parallel thread (also abbreviated NPS). Whereas NPT fittings may not need a sealant in order to be air or water tight, NPS fittings must be sealed with PTFE tape or dope
  • U.K. - The thread used for fittings is BSP which stands for British Standard Pipe Thread, defined in BS EN 10226-1 and BS EN ISO 0228-1. The most common sizes encountered in the home are 3/8, 1/2, 3/4 and 1 inch. These sizes originally referred to the inner diameter of a steel pipe for which the fitting was intended. Copper and plastic tube used with these fittings has been metric since 1971. The most common sizes are 10, 15, 22 and 28 mm for domestic applications. The size refers to the outside diameter of the tube.
  • Ireland - Threads on fittings are BSP. Tube sizes are imperial and normally quoted by referring to the BSP thread size of the corresponding fitting, e.g. 1/2, 3/4, 1 inch. The outside diameter of plumbing tube is slightly less than the corresponding British versions which can lead to issues with leaks if fittings and tube are mixed and matched. (See table below)

FIP and MIP meaning Female Iron Pipe and Male Iron Pipe respectively are terms sometimes used to refer to the gender of the threads used on a fitting.

For more info and sizes, see

NPT Pipe, Thread and Tube Sizes

NPT thread and nominal pipe sizes
NPT thread and nominal pipe sizes | Source

BSP Pipe, Thread and Tube Sizes

BSP thread and trade pipe sizes
BSP thread and trade pipe sizes | Source

How to Cut Copper or Plastic Pipe

Copper or plastic pipe can be cut with a hacksaw. However if you use a pipe cutting tool, it gives a cleaner, squarer cut without burrs. The type in the video below can be used to cut copper pipe. It can cut plastic pipe also with a little bit of effort, however a plastic pipe cutting shears does a better job.

File off any burrs on copper pipe after cutting if you use a hacksaw.

Cut tube with a pipe cutter
Cut tube with a pipe cutter | Source
Existing plumbing may need to be cut with a hacksaw if there isn't enough clearance to use a pipe cutter
Existing plumbing may need to be cut with a hacksaw if there isn't enough clearance to use a pipe cutter | Source
Use a file or de-burring tool to remove any sharp edges if you cut pipe with a hacksaw
Use a file or de-burring tool to remove any sharp edges if you cut pipe with a hacksaw | Source

Bending Copper Pipe

There are several techniques for bending copper pipe. You can't just grasp the two ends and bend, because the pipe will kink in the middle.

  • Use sand to prevent kinking This is an old technique which uses sand to prevent the pipe from kinking. The pipe is tightly packed with fine dry sand, and tightly plugged at the end with kitchen towel or a rag. The pipe is then bent to the desired shape.
  • Use a bending spring A bending spring can be used for making single bends in pipe. This method is only suitable for bending reasonably long lengths of pipe so that the length of the pipe can be used for leverage during bending. The spring is slid into the pipe so that it extends beyond the bend point. If necessary, a string can be tied to its end so that it can be retrieved. The pipe is then bent over the knee (just under your kneecap)
  • Use a pipe benders This tool has long levers to aid bending and enables one or more bends to be made in pipe. It also has several dies or guides to allow various diameters of pipe to be bent.

Pipe benders suitable for 15 and 22 mm copper tube, available from the UK tool distributor, Draper Ltd
Pipe benders suitable for 15 and 22 mm copper tube, available from the UK tool distributor, Draper Ltd | Source
Use a bending spring and bend pipe just under your knee cap
Use a bending spring and bend pipe just under your knee cap | Source

How to Use a Compression Fitting

  1. Measure the tubing to be cut and mark with a felt tipped marker. If a fitting needs to be inserted into existing tubing (e.g. a T-joint for a branch off), a section of tubing must be removed. Sometimes marks are provided on the outside of the fitting, indicating the location of the shoulder inside the fitting which the tubing butts up against when inserted. This aids in working out how much of the tubing needs to be removed.This needs to be reasonably accurate if copper tubing is being used as it can be difficult to pull the two ends of the tubing apart to insert the fitting if too short a section is removed, or difficult to pull the ptwo sections of tubing together again if too much tubing is cut out. Temporarily remove any clips holding the tubing so that the sections can be moved apart easier.
  2. Cut the tubing to be joined to the correct length. Ideally use a pipe cutter which gives a square, smooth edge. Alternatively use a junior hacksaw. Try to cut the tubing square, and file the cut edges smooth.
  3. Slide the compression nut over the end of the tubing followed by the olive ring.
  4. If plastic pipe is being used, push an insert into the end of the pipe. This prevents the pipe from being crushed by the olive as the compression nut is tightened.
  5. Push the tubing as far as it will go into the fitting.
  6. Tighten the compression nut until hand tight.
  7. Mark the nut with a felt tipped marker.
  8. You need 2 tools, one to to hold the fitting and the other to tighten the compression nut. You can use open ended wrenches, vice grips or water pump pliers. Make sure the tools are properly sized and grip tightly so that they don't slip off while tightening. Watching the mark on the nut, tighten it by 1/2 to 1 turn. If possible you can tighten by 1/2 turn, turn on the water supply and wait for a few minutes see if the joint "weeps". If this is the case, try tightening further. It's important to not over tighten as this can deform the olive, preventing it from sealing properly and causing a leak. Knowing how much to tighten a nut is learned by experience and as a rule of thumb, once the nut suddenly becomes difficult to turn, it is tight enough.

Typical compression fitting. This T-fitting allows a branch to be made in a pipe
Typical compression fitting. This T-fitting allows a branch to be made in a pipe | Source
Use an insert for plastic pipe
Use an insert for plastic pipe | Source
Fit the compression nut onto the pipe....
Fit the compression nut onto the pipe.... | Source
....followed by the olive ring
....followed by the olive ring | Source
Push the pipe fully into the fitting
Push the pipe fully into the fitting | Source
Tighten the compression nut by hand
Tighten the compression nut by hand | Source
Mark the nut with a felt tipped marker
Mark the nut with a felt tipped marker | Source
Tighten 1/2 to 1 turn with a wrench, Stilsons or water pump pliers. Hold the fitting also to prevent it turning
Tighten 1/2 to 1 turn with a wrench, Stilsons or water pump pliers. Hold the fitting also to prevent it turning | Source

How to Use Push Fittings

These vary somewhat, but in general this is the procedure

  1. Measure, mark and cut the pipe. In general you should avoid using a hacksaw as a square cut on the end of the pipe is more critical. Use a proper pipe cutter suitable for copper or plastic pipe. File off any burrs on the end of copper pipe.
  2. If using plastic pipe, push an insert fully into the end of the pipe
  3. Slide the pipe into the fitting until it will go no further. Pull back to ensure the teeth on the collet insert in the fitting have gripped the pipe and it is secure.
  4. Some fittings have a twist lock feature which prevents inadvertent release of the pipe if the collet is accidentally pushed back against the fitting. If this is the case, twist the screw cap on the fitting about half a turn. This further compresses the O-ring in the fitting and locks the teeth.
  5. Fittings can be disassembled when new by turning the twist lock counter-clockwise, pushing the collet back against the fitting body and pulling on the pipe. This retracts the collet teeth so that the pipe can be removed. Some fittings require the use of a key to retract the collet.

The video below shows how to use Speedfit twist lock fittings. These are very convenient to use for connecting both copper and plastic pipe.

How to Use a Speedfit Standard Twist and Lock Fitting

How to Use a Capillary Fitting With Copper Pipe

Capillary fittings require some skill in order to be assembled properly, however they are the cheapest, neatest and strongest solution for joining copper pipe.
Copper pipe and capillary fittings are "sweated" together. This involves heating the pipe and fitting so that solder melts and holds the joint together.

  1. Mark and cut the pipe using a hacksaw or pipe cutter. Remove any burrs with a file.
  2. Clean the inside of the fitting and outside of the pipe with wire wool until both are shiny.
  3. Apply flux to the inside of the fitting and outside of the pipe.
  4. Insert the first pipe into the fitting until it goes no further. Insert remaining pipes into the fitting. (All pipes should be soldered together rather than one at a time)
  5. If a Yorkshire fitting is being used (which has an integral ring of solder in each port), heat all around the fitting until a shiny ring of solder appears at the edge of the entry port on the fitting. Solder free fittings should be heated and solder wire applied to the edge of the entry port so that it flows into the gap between the fitting and pipe. (make sure it is lead free solder if the the water is for potable (drinking) use)

Warning: Be careful when using a blowtorch and take suitable precautions to avoid starting a fire. Adjacent plastic plumbing and wiring can easily be melted. Fireproof mats are available for placing behind fittings during heating. A ceramic tile can also give some protection, but avoid directing the flame directly on it as it can shatter

Capillary fitting. Notice the integral ring of solder
Capillary fitting. Notice the integral ring of solder | Source
Clean the pipe and inside of the fitting with wire wool and coat with flux
Clean the pipe and inside of the fitting with wire wool and coat with flux | Source
Heat the fitting with a blowtorch until a ring of solder appears. Fittings without an integral ring of solder must be "fed" with solder wire
Heat the fitting with a blowtorch until a ring of solder appears. Fittings without an integral ring of solder must be "fed" with solder wire | Source

How to Use Screwed Plumbing Fittings

Steel pipe with a screwed end, normally has a tapered male thread which mates with a female thread on the other fitting. PTFE plumbing tape or other proprietary thread sealing cord wrapped around the threads, increases lubrication and enables the male thread to be screwed in tighter to produce a watertight seal. The secondary benefit of the tape is to fill the gap between the female and male thread, helping to seal the joint. You can also smear pipe dope (jointing compound) over the tape on the joint to improve sealing in case the tape catches on the threads and rolls around as the fitting is being screwed into place. Traditionally hemp and jointing compound (Boss White, Plumbers Mait) were used for sealing joints. For some applications, if temperature is excessive, PTFE tape may be unsuitable and jointing compound can be used.
Sometimes both male and female threads are parallel in which case they are supposed to be sealed using a fiber washer or O-ring which is compressed by a flange on the fitting. This is often the case with a spigot (outside tap) or a hot water tank. A tapered fitting would possibly result in the fitting tightening suddenly with the spigot at the wrong angle. A washer however allows more leeway as regards tightening the fitting to the correct angle

  1. Hold the fitting or pipe and starting at the inner end of the threads, wrap PTFE tape tightly and evenly clockwise and upwards in a helical fashion until all but the last thread is covered. Leaving the first thread bare makes it easier to get the thread started during assembling of joints.
  2. Continue to wind the thread clockwise and downwards to where you started.
  3. Wind a third layer onto the fitting
  4. Screw the male thread into the female union

There is a certain degree of trial and error when winding tape onto fittings. If they are made to a tight tolerance, only a few layers of tape may be needed. Sometimes if fittings are a loose fit, extra tape may be needed (4, 5 or 6 turns).

This Compression T-fitting has a 1/2 inch female screw thread.  The lower image shows a 1/2 inch to 1/4 inch reduction bushing which could be used for connecting a pressure gage for instance
This Compression T-fitting has a 1/2 inch female screw thread. The lower image shows a 1/2 inch to 1/4 inch reduction bushing which could be used for connecting a pressure gage for instance
Wind the tape clockwise, neatly and tightly around the threads. About 3 layers should suffice
Wind the tape clockwise, neatly and tightly around the threads. About 3 layers should suffice | Source
Screw the bushing into the fitting and tighten with a wrench
Screw the bushing into the fitting and tighten with a wrench | Source

Wrapping Thread Seal Tape

Did You Find This Article Useful?

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Opinions and corrections from pro plumbers are welcome!

Questions & Answers

    © 2015 Eugene Brennan

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      • profile image

        Hastadur Pun 2 months ago

        Very useful article

      • eugbug profile image
        Author

        Eugene Brennan 3 months ago from Ireland

        Hi Richard,

        This may be of use to you:

        https://en.wikipedia.org/wiki/National_pipe_thread

        I did a Google image search using these terms, it might help you find what you need:

        npt pipe fitings 3/16 elbow compression to female

      • profile image

        Richard Murphy 3 months ago

        Are steel tube fittings and copper tube fittings the same thread, NPT? I am trying to find a Fitting to connect a Steel Heat Riser Tube to my Autolite 4100 Carburetor's Choke. The Compression Nut measures .1875" = 3/16" x 24 and this Nut fits on the Cast Fitting on my Carb's Choke. BUT this cast fitting points toward the Firewall at a 45 degree down angle. I need it to point toward the right/passenger side wheel well. A 90 degree street elbow with the 3/16" (with a Female NPT is what +

        ++++I THINK is what I need.the Compression Nut, Olive Ring and Steel Tube are .1875" = 3/16".) I can find a 90 Elbow that is 3/16" Compression on one end but CANNOT find a 3/16" FPT for the Choke end. I THINK the cast fitting on the Choke is NPT and I need a Female on the Choke end. OR maybe 2 fittings that would accomplish the same thing. Can you confirm that Steel Tubing and Copper Tubing fittings both have NPTs? Might you know of a source for this (apparently) oddball fitting?

        I have spent yesterday and today searching the web with no results. Murphy's Law = and I am Murphy! Thank you, Murf

      • eugbug profile image
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        Eugene Brennan 14 months ago from Ireland

        Loctite 55 pipe sealing cord is supposed to be good for sealing and locking a tap in place. It allows a 45 degree realignment which isn't possible with PTFE tape. An alternative is to use hemp and jointing compound. Another suggestion I've come across is to form a taper on the threads when winding PTFE tape. This is so that instead of having parallel threads, you now have a taper which will wedge tightly as you tighten.

        It's actually better to feed the supply line into tap from above because in freezing conditions, the shut off valve indoors can be turned off, and the tap turned on to drain the line and tap body. If the feed is from below, everthing will stay filled up and freeze.

      • profile image

        Woking Mike 14 months ago

        With regard to your picture of the brass tap and the wallplate; it would be helpful to explain how to deal with the fact that when you screw the tap onto the wallplate it finally tightens with the tap at a random angle. With the 15mm pipe coming up into the compression joint, how do you make the tap tighten when it is pointing downwards.