A Pipe Thread Dimensions Chart is a reference table that provides the standard dimensions of pipe threads, including nominal pipe size, outside diameter (OD), threads per inch (TPI), pitch, and thread type. These charts help engineers, plumbers, machinists, marine engineers, and maintenance technicians select the correct fittings and ensure leak-free pipe connections.
Using the correct pipe thread dimensions is essential because pipe threads are designed to seal fluids and gases under pressure. Even a slight mismatch in thread profile or diameter can result in leaks, damaged fittings, or equipment failure.
A pipe thread chart helps you:
Whether you work in marine engineering, oil & gas, plumbing, hydraulic systems, or manufacturing, a pipe thread dimensions chart is an essential reference.
The most commonly used pipe thread standards are:
Thread Standard | Full Form | Common Regions | Thread Angle | Thread Type |
BSP | British Standard Pipe | Europe, Asia, Australia | 55° | Parallel (BSPP) & Tapered (BSPT) |
NPT | National Pipe Thread | USA & Canada | 60° | Tapered |
NPTF | National Pipe Thread Fuel | USA | 60° | Dry Seal Tapered |
Metric | ISO Metric Thread | Worldwide | 60° | Parallel |
The two most widely used standards are BSP and NPT, but they are not interchangeable because they differ in thread angle, dimensions, and sealing method.
The following table shows the commonly used BSP thread sizes.
Nominal Size | Threads Per Inch (TPI) | Major Outside Diameter (mm) | Major Outside Diameter (inch) |
1/8″ | 28 | 9.73 | 0.383 |
1/4″ | 19 | 13.16 | 0.518 |
3/8″ | 19 | 16.66 | 0.656 |
1/2″ | 14 | 20.96 | 0.825 |
3/4″ | 14 | 26.44 | 1.041 |
1″ | 11 | 33.25 | 1.309 |
1¼” | 11 | 41.91 | 1.650 |
1½” | 11 | 47.80 | 1.882 |
2″ | 11 | 59.61 | 2.347 |
Typical BSP dimensions based on ISO/BS standards.
The following table lists the standard NPT thread dimensions.
Nominal Size | Threads Per Inch (TPI) | Outside Diameter (mm) | Outside Diameter (inch) |
1/16″ | 27 | 7.94 | 0.313 |
1/8″ | 27 | 10.29 | 0.405 |
1/4″ | 18 | 13.72 | 0.540 |
3/8″ | 18 | 17.15 | 0.675 |
1/2″ | 14 | 21.34 | 0.840 |
3/4″ | 14 | 26.67 | 1.050 |
1″ | 11.5 | 33.40 | 1.315 |
1¼” | 11.5 | 42.16 | 1.660 |
1½” | 11.5 | 48.26 | 1.900 |
2″ | 11.5 | 60.33 | 2.375 |
Typical NPT dimensions based on ASME B1.20.1.
Follow these simple steps:
Step 1: Measure the Outside Diameter
Use a vernier caliper to measure the outside diameter of the male thread.
Step 2: Count the Threads
Use a thread pitch gauge to determine the Threads Per Inch (TPI).
Step 3: Check the Thread Type
Determine whether the thread is:
Step 4: Compare with the Pipe Thread Dimensions Chart
Match:
This allows accurate identification of the pipe thread.
One common misconception is that the nominal pipe size equals the measured thread diameter.
For example:
A 1/2-inch BSP thread has an outside diameter of approximately 20.96 mm, while a 1/2-inch NPT thread measures approximately 21.34 mm.
The nominal size refers to the approximate internal bore of the original pipe standard rather than the actual thread diameter.
Avoid these frequent errors:
It is a reference table showing pipe thread sizes, outside diameters, thread pitch, and other dimensions used for identifying and selecting threaded pipe fittings.
BSP threads have a 55° thread angle and may be parallel or tapered, while NPT threads have a 60° angle and are tapered. They are not directly interchangeable.
Nominal pipe size refers to the historical approximate internal bore of the pipe, not the measured thread diameter.
No. Although some sizes have similar thread pitches, differences in thread angle and profile can cause leaks and damage.
Measure the outside diameter, determine the thread pitch (TPI), identify whether the thread is parallel or tapered, and compare the measurements with a standard pipe thread dimensions chart.
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