How To Determine Pipe Thread Size And Pipe Type? A Straightforward Guide

Thread sizes are nominal and do not correspond to conventional units of measurement. Therefore, it is difficult for you to measure the pipe thread size to determine the exact type of thread.

If you do not choose the correct type of pipe thread, it will cause problems with the repair and installation of the device. To help you avoid misunderstandings and install properly, this article will show you how to determine pipe thread size and pipe type.

What Are The Common Pipe Thread Types?

How To Determine Pipe Thread Size And Pipe Type

What Are The Common Pipe Thread Types?

  • NPS or NPT (national pipe straight or tapered): These types are the most prevalent in North America.
  • Compression: A special threaded fit that does not match other types of thread.
  • FIP or MIP (female or male iron pipe): The following thread diameters are the same as BSP(S) or NPT BSP(T), and they are most common in Europe.
  • UNS (National Unified Special): Some of them are suitable with compression accessories.

Of course, you could tighten the threads. However, when they don’t fully match, your fittings won’t seal. The majority of pipe threads are not interchangeable. MIP, FIP, and NPT function in conjunction with other kinds. In a sense, a BSP does not fit an NPT. 

The match itself often tells you the sort of thread you need. On the top, the lettering can be engraved or imprinted.

How To Determine Pipe Thread Size And Pipe Type?

How To Determine Pipe Thread Size And Pipe Type

How to Determine Pipe Thread Type and Pipe Size


Make sure you have two tools available to detect the threads before you begin working on determining pipe thread type and pipe size:

Pitch Gauge

A pitch measuring is an instrument for measuring the length between thread peaks. We check the number of threads per inch with BSPP, BSPP, UN/UNF, and NPT. When you have a metric gauge, the pitch measuring indicates in millimeters the distance between each peak.


The thickness of a thread is measured with a caliper. It metrics the outer diameter of a male thread and the interior diameter of a female thread. A digital caliper is compatible with a variety of shops for more sophisticated users. It minimizes your time and facilitates the process.

Guide Steps

Step 1: Determine what you are going to use the fitting for?

How To Determine Pipe Thread Size And Pipe Type

Determine what you are going to use the fitting for? 

Suppose you reside and buy an NPT to install on your coffee maker in the United States. Nevertheless, you didn’t understand that your coffee-making machine was built in Italy and only required BSP fittings. You may run a risk of ruining the threads on your system if you try to twist the NPT thread into the BSP, and unfortunately, such harm often cannot be remedied.

It would be challenging for you to determine if your machines don’t display the thread type when you just have a BSP or NPT by looking at the thread. You may probably need to install the NPT if you live in the U.S. And in case you reside in Europe, BSP will be what you need. To identify the kind of fittings, you may always gauge the threads or test several varieties.

Step 2: Determine whether you need a male or female fitting? 

As mentioned above, threads are interestingly both male and female in gender. Male fittings have threads on the exterior, whereas female fittings have threads on the inside. Because the male end pushes into the female end, the outside diameter of a male thread is less than that of a female thread.

Step 3: Determine whether the threads are tapered or straight? 

This is a very important step to determine how to determine pipe thread type and pipe size.

National pipe straight (NPS) and national pipe tapered (NPT) are two different types of pipes. Straight threads have the same diameter as tapered threads as they expand outward.

Straight attachments do not have a tapper and are secured by an O-ring or gasket to another attachment. At the end of the fitting, both males and females are flared, enabling them to screw together and produce a close seal. As the male and female ends fit into each other, the threads interlock.

Tapered and straight accessories require a seal to avoid leakage. A straight-fit male end has to be sealed with a washer, O-ring, or joints. Pipe dope, Teflon tape, or any other pipe sealant should be attached to a tapered attachment.

To ensure that your connection is strong, you must have the proper partner. You can only get certain threads deep when you try to thick a tapered fit into a straight fit. The seal between the fittings will not be strong enough to prevent leaks, even if they appear to fit firmly together.

Step 4: Determine the fitting thread size or pipe size.

For many homeowners, the most difficult element is determining pipe thread size because thread measurements aren’t based on traditional units of measurement. The pipe’s ID is depending on the thread dimensions. You could use a measuring tape, ruler, or caliper to determine the thread diameter of a male or female thread. Measure the internal thread diameter (ID) with the outside thread diameter (OD). This value helps to calculate the dimension of the thread.

Step 5: Determine what pipe fitting is compatible? 

Finding the appropriate pipe fitting is analogous to picking the correct Lego while assembling a Lego set. Your project would decide the layout of your fittings. 

You might want to prevent leaking spots when you walk around the back of the cabinet to reach the ice-maker or attempt to hide tubing. The form or style of pipe fitting you select depends on where you need the water, fluid, or air to go—around a corner or up a pipe.

Note: Pressure loss and a reduced flow rate might occur with numerous fitting elements, curves, or elbows.

What Are The Common Pipe Thread Materials To Choose?

How To Determine Pipe Thread Size And Pipe Type

What Are The Common Pipe Thread Materials To Choose?

Understanding common pipe thread materials to choose from is also essential after knowing how to determine pipe thread type and pipe size.

Along with piping materials, we select the materials for pipes. Flexibility, cost, environmental conditions, needed pressure ratings, and medium are all elements to consider while making a decision. The options for materials include various metal or plastic kinds.

Let’s take a look at the common metals included:


Thanks to its lightweight and resistance to corrosion, aluminum is a popular plumbing material and the recommended fitting element for aluminum pipes. Aluminum alone has poor tensile strength and is utilized when great corrosion resistance is required. To increase strength and durability, it is combined with silicon, copper, manganese, zinc, and other metals.


With excellent conductivity and high-temperature flexibility, this material is robust, corrosion-resistant, and strong. Because of its high-performance qualities and machinability, brass is frequently utilized for smaller compression and threaded pipe fittings. Brass connections could have a variety of preventative or ornamental coatings that would suit the pipe’s finish.

Cast iron

Cast iron is highly resistant to abrasion and strong. Because of its resistance to abrasiveness elements such as gravel, sand, debris, and solid waste, cast iron fittings and pipes are used mainly for the storm drain, construction of sanitary, ventilating, and waste applications.


Copper is known for its high corrosion resistance and good electrical conductivity. For many plumbed and heated applications, copper fitting is vital and is widely used for domestic water supply lines. Copper fittings, which can be soft or stiff, are commonly used in combination with copper pipes. The only copper appropriate for flare connections is soft or ductile copper, which can be bent and manipulated easily. Hard copper is not flexible and requires directed access to corners and barriers.


Sustainable, robust, and heat resistant are some characteristics we must mention when ỉt comes to steel. Steel is an iron-carbon combination that is frequently alloyed with other metals to increase oxidation ductility and toughness. 

Combustible gases, water, and other fluids are transported using them for both industrial and commercial purposes. For resistance to rust and chemical corroding, galvanized steel is coated with zinc. Carbon steel is combined with greater amounts of carbon to enhance strength and elasticity.

Stainless steel

It is quite robust and has high oxidation and corrosion resistance. Stainless steel is a steel alloy containing more than 10.5% chromium, which provides high corrosion resistance for hygienic applications and those working with hostile fluids and chemicals.

The following are examples of common plastics: 

PVC (poly-vinyl-chloride)

Pipe fittings are commonly made of this type of plastic. PVC is a material that is hard and may be used under various pressures. Connected fittings are through solvent welding (glue) or threading. Coldwater supply and sewerage systems are common uses.

ABS (acrylonitrile butadiene styrene)

ABS is hard and black plastic with similar characteristics and PVC use. However, it is usually more cost-effective.

Polyethylene (PE)

For warm and cooler applications, Polyethylene is the most recommended plastic. PE is a semi-flexible plastic that comes in two colors: black and grey. Sprinkler system supply lines and subsurface geothermal heating loops both utilize fittings.

Polypropylene (PP)

Bi-axial strength, yield elongation, and cold flow characteristics are all outstanding in this thermoplastic material. It’s comparable to PVC; however, it may be utilized in outdoor applications because of its resilience to UV, ozone, and weathering.


If you are looking for a plastic material that is highly resistant to corrosion and chemicals, nylon would be a nice option. Because nylon can be used with combustible fluids, chemical solvents, and drinkable water, it is the ideal plastic.

Tip: Make sure the system fluid and any recommended fitting materials are compatible. Corrosion might lead to leakage or harm to the system if incompatible.

What Are the Tips For Assembling Pipe Fittings?

How To Determine Pipe Thread Size And Pipe Type

Assembling Pipe Fittings with Useful Tips

  • Do not thread your threads through. It’s cross-threading or going in at an angle if you are inserting a fitting, and it seems like it’s going in wrongly.
  • To screen threads for easier installation, use Teflon rubber rather than pipe dope. The dope of the pipe could be sloppy and might spill into the filter housing or equipment if you use too much. Make sure that you test the seal to make sure it is effective after applying the sealant.
  • Before using your fittings, you had better clean the ends of them. You don’t want to catch any of the debris in the threads. right?
  • Overtightening the fitting will cause it to break or split. When utilizing plastic fittings, this is extremely difficult.

Final Thoughts 

After reading the detailed guide above, you must already know how to determine pipe thread type and pipe size.

Fittings might be extremely confusing. When they don’t fully match, then your fittings won’t seal. They must have internal diameters large enough to fit over the pipe’s exterior diameter. Besides, flexibility, cost, environmental conditions, required pressure ratings, and means are important elements to decide on suitable materials.

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