Hoses are now the most common tools that you work with almost every day. Have you ever wondered how these hoses are connected to fittings, other pipes, or equipment? The answer lies in the thread. But the right thread size matters a lot, and this is where many beginners get confused. To resolve this confusion, those thread size charts come into play.
Remember, if you choose the wrong thread size, you’ll get leaks and wasted material. That’s why choosing the right thread size is of utmost importance. But if you are new to this term, then some numbers and abbreviations might seem challenging. If so, worry not! In this guide, I will explain everything about the hose thread size chart. So let’s get started.
What Is Hose Thread?
Before discussing the thread size chart, let’s first understand the hose thread itself.
A hose thread is the spiral-shaped groove you can find at the end of a hose or fitting. It helps the two parts screw together and create a secure connection. These threads allow hoses to attach tightly to taps, pipes, or equipment so that fluids can flow without leakage.
No doubt, the hose thread is like a spiral groove. However, it does not mean that all are of the same size. Instead, they come with specific sizes and patterns. For example, some threads are straight, while others are slightly tapered. Similarly, some of those threads require a washer to stop leaks, while others seal tightly on their own.
This is why even two threads that look the same may not connect properly. That’s why choosing and identifying the right thread size is crucial. If there is a slight difference between the hose thread and the fitting, it will cause leaks and weaken the connection.
Types of Hose Threads
In real-world applications, hoses are used in many different environments. Right? That’s why there are different types of threads to meet those different needs. Therefore, before understanding the thread size, first understand its types as follows.
1- Garden Hose Thread (GHT)
The most commonly used hose thread type is garden hose thread. In fact, you will find these threads on garden hoses, outdoor taps, and watering tools. Moreover, a GHT is designed to make it easier for you to connect and disconnect the hose without a special tool. Typically, in most cases, the standard home size is 3/4-inch GHT.
But remember, garden hose threads are straight, not tapered. This means the threads do not tighten on their own to stop leaks. Instead, you have to place a small rubber washer inside the connector to create a seal. Therefore, GHT hose threads are considered ideal only for low-pressure applications.
2- National Pipe Thread (NPT)
National Pipe Thread (NPT) is another thread type mostly used in plumbing and industrial systems. Unlike GHT, these threads are tapered. As a result, the diameter gradually becomes smaller as the threads go deeper. Therefore, when you screw in an NPT fitting, it creates a strong seal without a washer.
Even the high pressure inside the gas or liquid does not affect the seal. That’s why they are preferred for gas lines and industrial hoses, where a reliable, tight connection is required. At this point, note that you cannot connect NPT to GHT even if they are the same size. This is because of the difference in the angle.
3- National Pipe Straight Mechanical (NPSM)
National Pipe Straight Mechanical (NPSM) is a straight hose thread. It means the threads’ diameter remains constant throughout their length. That’s why they need a gasket or washer to create a seal; they cannot do so on their own. You might wonder if it is GHT, but that’s wrong.
The GHT requires hand tightening and is used for household garden hoses. However, NPSMs are commonly used in hydraulic hoses and industrial connections. They usually don’t hand-tighten; they require a basic tool for precise tightening. That’s why we can say that even though GHT and NPSM are straight, they are not compatible and cannot be connected.
4- British Standard Pipe (BSP)
British Standard Pipe (BSP) is a widely used thread type, especially in countries outside the United States. Generally, these hose threads basically come in two types. The first one is a BSPP (parallel/straight) thread that requires a washer or gasket for sealing. The second type is BSPT (tapered), which provides a strong seal on its own.
Remember, these threads are designed with a specific angle and pitch. Therefore, they are compatible with the BSP standard but are incompatible with NPT threads, even though they have the same size. Another interesting aspect of BSP is its versatility. As you can see, both straight and tapered versions are available; they can be used in low- and high-pressure hoses.
What is a Hose Thread Size Chart?
Now that you have a basic understanding of hose threads and their types, let’s understand the hose thread chart.
A hose thread size chart is a simple guide that shows the different sizes, types, and measurements of hose threads. It helps you quickly identify which thread will fit a particular hose or fitting in your system. Using this chart, you ensure that connections are secure, leak-free, and compatible.
In simple words, a hose thread chart is a reference that helps you choose the correct hose connection without guesswork. In this chart, you will come across three parameters. Therefore, before you look at the chart and make a selection, here are the terms you must understand.
- Nominal Size: The nominal size is the “name” of the hose thread, like 1/2 inch, 3/4 inch, or 1 inch. It is basically used as a standard reference to identify the thread. However, don’t confuse it with the actual measurement of the hose fitting. It is just like a label to make it easier to compare sizes.
- Outer Diameter (OD): The outer diameter (OD) is the actual width of the thread measured from the outer edges. It tells you the true size of the hose or fitting. As a result, you ensure that the two parts will fit together correctly.
- Thread Pitch (TPI): The thread pitch is the number of threads in one inch of the fitting. That’s why it is often called Threads Per Inch (TPI). Remember, a hose with a higher TPI has threads closer together. However, a hose with a lower TPI has threads that are farther apart.
A Basic Hose Thread Size Chart
Here is the thread size chart that you can follow.
| Thread Type | Nominal Size | Outer Diameter (OD) | Threads Per Inch (TPI) |
| GHT (Garden Hose Thread) | 1/2″ | 0.840″ (21.3 mm) | 14 |
| GHT | 3/4″ | 1.05″ (26.7 mm) | 11.5 |
| GHT | 1″ | 1.315″ (33.4 mm) | 11.5 |
| NPT (Tapered) | 1/8″ | 0.405″ (10.3 mm) | 27 |
| NPT | 1/4″ | 0.540″ (13.7 mm) | 18 |
| NPT | 3/8″ | 0.675″ (17.1 mm) | 18 |
| NPT | 1/2″ | 0.840″ (21.3 mm) | 14 |
| NPT | 3/4″ | 1.050″ (26.7 mm) | 14 |
| NPT | 1″ | 1.315″ (33.4 mm) | 11.5 |
| NPSM (Straight) | 1/2″ | 0.840″ (21.3 mm) | 14 |
| NPSM | 3/4″ | 1.050″ (26.7 mm) | 14 |
| BSPP (Parallel) | 1/2″ | 0.825″ (21 mm) | 14 |
| BSPP | 3/4″ | 1.035″ (26.3 mm) | 14 |
| BSPT (Tapered) | 1/2″ | 0.825″ (21 mm) | 14 |
| BSPT | 3/4″ | 1.035″ (26.3 mm) | 14 |
How to Measure Hose Thread Size: Step-by-Step Guide
The thread chart alone is not enough to choose the hose thread. Before that, you have to take some measurements. Here are a few steps you can follow to measure the correct hose thread size and choose the right fitting.
Step 1: Measure the Diameter
First, measure the outer diameter (OD) of the hose thread. As mentioned above, it is the width of the threads measured from the outer edges. To do this, take a ruler, caliper, or tape measure. Then, start measuring from the outer edge of one thread to the outer edge on the opposite side.
You will see that this measurement will come in inches or millimeters. This diameter will give you a basic idea of the size, but don’t rely on it alone. Why? Because different thread types can have the same diameter but different pitches or angles.
Step 2: Count Threads
Once you have the OD measurement, the next step is the thread count, which is Threads Per Inch (TPI). Start counting the number of threads along one inch of the fitting using a ruler. If your fitting has 14 TPI, it means there are 14 threads per inch of the hose.
Also, remember that even if two hoses have the same diameter, the threads won’t fit together if the TPIs differ. But what if the threads are shorter than an inch? In this case, you just have to count the number of threads in that part and estimate how many would fit in a full inch.
Step 3: Identify Thread Type
Once you have the diameter and TPI, identify the thread type. As I said above, hose threads can be tapered or straight. Each of these has its own angle. Right? For example, GHT and NPSM are straight threads. NPT and BSPT are tapered threads, and BSPP is parallel/straight. Now, understand which thread type you have. It will help you determine how the seal is made.
Step 4: Match with the Chart
Finally, measure the diameter of your hose and count the threads per inch (TPI), then match the chart. This chart lists all common hose threads, along with three main measurements. For example, it contains normal sizes, outer diameter, and TPI. Now find the row in the chart where the diameter matches your measured OD and the TPI matches your thread count.
The chart also tells you the thread type (GHT, NPT, NPSM, BSP). Then, when you match both the diameter and TPI to a row in the chart, you will know the exact size and type of your hose thread. Therefore, this size will now help you choose the right thread size of fitting to ensure leak-proof sealing.
Frequently Asked Questions
Why do some threads not match?
Some threads may not match because they have different types, diameters, or thread pitches (TPI). If these factors don’t align, the threads won’t fit together properly. This will result in leaks or loose connections.
Why does my hose leak even if the diameter matches?
Even if the diameter looks the same, the threads might have a different pitch (TPI) or type. For example, straight threads like GHT need a washer or gasket to seal. However, tapered threads like NPT seal by themselves. If the wrong type is used or if the washer is missing, the hose will leak.
Can a hose thread chart help me buy fittings online?
Yes! A hose thread chart shows the thread type, diameter, and pitch for all common hoses. Therefore, you can match our hose measurements to the chart and choose the correct fitting online.
Conclusion
Let’s conclude: Hose are a must-have in several industries, from oil and gas to household and machinery. The fluid and liquid transportation becomes less of a hassle. However, the correct hose thread size is crucial to ensure a leak-proof connection.
Many people, especially newbies, get confused about the thread size. They end up choosing the wrong hose thread size, resulting in a misfit. This is where the hose thread size chart comes in handy. This guideline contains important measurements, such as thread type, TPI, and outer diameter. From this chart, you can confidently identify the right hose thread size for secure connection.