Brief Introduction to Thread Standards
When selecting a pipe, fitting, or nozzle, you will notice that they have different threads at their ends. Measuring their sizes will not guarantee you of finding the right match to the component you’re going to connect them to. This is where thread standards come in.
Whether you’re looking for a male or female thread, tapered, or parallel, the codes will be different depending on your location. Countries follow different standards and they have different dimensions. Learning what threads are and the different thread standards will help you find the exact thread match for your project.
What Are Screw Threads?
Screw threads, or simply threads, are designed to connect components together. They have helical structures for converting linear and rotational force or movement. They are ridges covered around a cone or cylinder.
The male or external thread is the helical thread wrapped around a cone or cylinder that you can find in screws, bolts, and studs. You can find the female or internal thread in one of the components, like tapped holes and nuts, that will connect to each other.
What Is the Importance of Thread Standards?
The main purpose of the standardization of threads is to guarantee compatibility and effective maintenance and repair. By finding the exact match, tight sealing is guaranteed that eliminates the chance of any leaking.
Common Thread Standards in Different Areas
Europe and the United States have their own thread standards which are also used in other countries. Ther are also other standards that many countries choose to follow. Let’s take a look at some of the most commonly used thread standards in the world:
1. ISO Metric Screw Threads
This is the standard widely used for general-purpose threads across the globe. Metric screw threads are made up of symmetrical V-shaped threads. Their sizes are specified as length, diameter, and pitch, in millimeters. They are categorized as coarse or fine. However, there are some sizes that are available in extra fine threads.
When the pitch is not included, it will safe to assume that the metric threads are coarse. They are more commonly used compared to fine metric threads. These threads are usually less coarse compared to the threads used in the United States. They also appear to be spaced more closely.
These threads are not that common and depending on their sizes, they can be more or less fine.
2. Unified Thread Standard – UTS
The UTS comprises the screw threads widely used in the United States and Canada. They are the standards used in nuts, bolts, and an array of threaded fasteners for these countries. It shares the same profile as the metric threads. However, the dimensions of UTS threads are in inch fractions rather than millimeter values.
3. American National Standard Pipe Thread
The National Pipe Thread may also be referred to as NPT (M), MNPT, or MPT with the M denoting male external threads. Meanwhile, NPT is also known as NPT (F), FNPT, or FPT for female internal threads. For these threads, a Polytetrafluoroethylene (PTFE) sealant is required at all times to prevent any leaking from the seal.
American National Pipe Tapered – NPT
The standard for tapered threads for joining pipes and fittings. The characteristics of NPT threads are the following:
- 60-degree thread angle
- Flat truncations of roots and crests
- The measurement for the pitch is TPI or threads per inch.
Here is a chart for NPT threads used for general purposes.
American National Standard Pipe Straight – NPS
NPS threads share similar shapes, angles, and pitches with NPT thread. They also have the same 60-degree angle and flat valleys and peaks. The difference is NPS threads are parallel, while NPT threads are tapered.
4. British Standard Pipe – BSP
The British Standard Pipe threads serve the same purpose as NPT threads. However, they are not interchangeable. They come in two types according to the thread type:
BSP Parallel (BSPP)
Commonly referred to as BSP, this refers to parallel threads that have a uniform diameter.
BSP Tapered (BSPT)
Also known as BSPT, it includes tapered threads that have diameters that increase or decrease along the thread’s length. You can combine these threads into two kinds of joints:
- Longscrew threads joints – This type uses parallel pipe threads and the tightness of the joint is accomplished through a sealing ring.
- Joining threads joints – In this type, tapered male threads are combined with either a parallel or tapered female thread. This will create a pressure-tight joint.
NPT vs BSP
It’s worthy to note the difference between NPT and BSP as there are many confusions regarding these threads.
In pipes and fittings, the American National Standard Pipe Thread standards are the technical standards used for screw threads in the United States. More known as NPT, they consist of both parallel and tapered series for a variety of purposes. These include tight sealing and rigidity.
The British Standard Pipe technical standards, commonly known as BSP, are the standards adopted internationally for connecting and sealing pipes and fittings. This does not include the United States as they follow the NPT standards.
NPT and BSP threads are not compatible and shouldn’t be used interchangeably. They differ in thread forms and have different pitches in most sizes. NPT threads have a 60-degree angle and have flat valleys and peaks. BSP threads have a 55-degree angle and have round valleys and peaks.
How to Identify Different Threads
Keeping up with all the different thread standards is a challenge. It’s important that you don’t make errors as this can lead to different problems. These can include losing money, wasting time, and compromising safety. To make sure you avoid these problems, here is a step-by-step guide to identifying the right thread standard.
Tools You Will Need
Before you start the steps in determining the thread standard, make sure you have the proper tools that will help you in this process.
The caliper is useful in measuring a male thread’s exterior diameter and a female thread’s interior diameter. It will help you come up with the most precise measurements. This tool is strongly recommended in identifying thread standards. However, if you don’t have one, you can use a straight steel ruler.
This tool will measure the threads per inch and will help you determine their pitch.
Step 1: Identify the Fitting’s Gender
Identify whether the fitting is male or female by locating the threads. The fitting is male if the threads are found on the outside. Meanwhile, the fitting is female if the threads are located inside the hex nut.
Step 2: Check If the Threads Are Parallel or Tapered
The next step is to identify whether the threads are parallel or tapered. Parallel threads will have the same diameter from both ends. If the diameter increases on the male end and decreases on the female end, then the threads are tapered.
Step 3: Identify the Size of the Threads
This time, identify the nominal diameter of the threads. You can achieve this by using a caliper. For parallel threads, you can measure any full thread, but for the tapered ones, measure the fourth or fifth full thread.
Step 4: Determine the Pitch
Determine the pitch of the threads from crest to crest. This is to see the number of crests there are in an inch of the thread. Use a pitch gauge and check the thread against each form until you find its match. To avoid mistakes, repeat the process and make sure you have the exact match.
Step 5: Determine the Thread Standard
The last step is to identify the thread standard. Gather all the information you have – the thread category, thread size, and the pitch. Refer to a thread identification guide and compare your info to find the right standard.
At The End
Finding the right thread match is essential. A simple mistake can lead to a mismatch that will further lead to serious problems. Taking note of the information above will help you find the right screw threads for your project. Once you find the thread you need, there’s one more step you need to accomplish. You need to find the right supplier to ensure performance and stability. With that said, check out Tubomart screw threads and other pipe needs today!