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IPS Vs NPT: What is The Difference?

When you get to the world of plumbing, you will encounter terms like IPS and NPT.

IPS stands for Iron Pipe Straight thread where the threads seal on a washer which is common with threads that hoses and toilet faucets attach to.

NPT stands for a National Tapered Thread and is also known as ANSI/ASME B1.20.1 pipe threads and are designed to seal on threads and plumbers use a pipe tape on the threads to provide lubrication for the formation of a seal.

IPS Versus NPT Pipe Thread Standards Differences

There has been a huge debate around the differences between IPS and NPT, so what is the difference? The most distinct difference is that the IPS sizing systems has a straight thread while the NPT has a tapered thread. Even though they look similar, they have different functionality and work differently in specific workspaces.

We are going to give an in-depth view of the two to give you a clear understanding of each of them and clear all the confusion.

IPS Pipe Connections

The IPS connection has been in use since the 19th century making it a very old system that has been tried and tested to near perfection. This system categorizes the thickness of pipe walls.

In the beginning the IPS pipe was mainly used in sizing wrought iron pipes. This system is still found in modern times iron, brass, steel and even the common PVC plumbing parts.

Do not be confused when you find FIPS or MIPS threading on most plumbing fittings as this is just a difference in the naming structure. They have all been derived from the IPS system.

Unlike in the past when the IPS connections were only found in the threaded fittings iron pipes, today there are numerous PVCs that use this connection.

The main reason for using the IPS is because the standard looks at the outer dimension of the pipe. This makes it a best suit for durable leak free household connections. It is commonly used in underground piping systems. The standard PVC has a similar external size with the common steel pipe.

Where are IPS Pipe Connections Used?

Surprisingly, both IPS and NPT parts fit together so you can use IPS pipe connection with NPT pipes. So where will IPS fittings work best?

To get a clear understanding we ought to look at the prominent performance characteristics. The IPS pipes have a very low thermal conductivity and power consumption. For this reason they are most preferred for hydronic heating systems.

The connections work best for hot water systems which helps in reducing heat losses. The fact that they are durable makes it a perfect fit for such connections.


NPT Pipe Connections.

This is a very unique measurement for pipe threads in the USA. It is also known as ANSI/ASME B1.20.1 standard.

This has been the most common connection in the US for the last 100 years. The NPT pipes are readily available and they are provided in different sizes and shapes too.

The NPT pipes have been largely accepted due to their ease of connection. You can easily connect the NPT pipes without flaring the seals, O-rings or the tubes.

Though the NPT pipes were designed for waterlines, many plumbers use them for hydraulic systems. Since they are not best suited for hydraulic systems they pause a great risk of leakages.

Where Can You Use NPT Connections?

The NPT connections are best suited for pipes used to transfer fluids and gas. Although it is a known fact that NPTs do not do well with fluid pressures from hydraulic systems, you can still use them but ensure you make a great choice.

You will easily find NPT pipes in your local store. If you are doing low pressure connections, go for brass or iron connections. If you are piping for high pressure connection use carbon or stainless steel pipes.

Leakage is a huge issue when it comes to high pressure and NPT pipes. This is because the pipes work on a principle of thread deformation which is a metal to metal sealing design. This makes NPT pipes perfect for one-time connection.

The NPT connections therefore work best for places where you won’t assemble today and disassemble tomorrow or have regular works. The reason being that if you keep disturbing the connection, the threads will soon deform and you will have multiple leakages.

IPT vs NPT Comparison

This is a simplified table to show the differences


Thread TypeStarightTapered
SizeCentered on the wall thickness and pipes inside diameterCentered on outside diameter and thread per inch
UseDomestic indoor and outdoor faucets, hydraulic water system agriculture systemUsed in Manufacturing industry natural gas lines, power plants, oil stations, gas staions and chemical supply compressed air lines.
SealsDoes not need PTFE tapesPTFE tape needed for sealing
AdvantagesThe PVC pipes and their fittings use IPS to form a water tight seal. Very long lasting connections.Widely and readily available. Easy time during assembly.




Having looked at the major differences between IPS and NPT it is now easy to make a choice when buying your pipes. You need to first investigate and know which pipes have been installed in your household then you can proceed to buy the fittings that match with the piping.