Thread table for cylindrical threads
Choosing the right type and size of thread is important for creating a tight, stable, and durable connection between hoses, pipes, fittings, and other components.
In the thread table below, you’ll find dimensions for several common thread standards, including BSP, NPT, metric threads, UNF, and ORFS. By measuring the thread’s diameter and pitch, you can compare the results with the table and more easily identify the thread type and size you have.
How do I use the thread table?
- Measure the thread's outer or inner diameter.
- Check the thread pitch or the number of threads per inch.
- Determine whether the thread is parallel or tapered.
- Compare the dimensions with the various thread standards in the table.
- Check that the dimension, pitch, and thread type are correct before selecting a component.
| Outside diameter | Increase | BSP (T) (K) R | Metric | UNF ORFS | SAIFA (UN thread) | NPTF/NPSM | Inside diameter |
|---|---|---|---|---|---|---|---|
| 9,3-9,7 | 28 GPT | 1/8” | 8,5 - 8,9 | ||||
| 9,3-9,7 | 29 GPT | 1/8” | 8,5 - 8,9 | ||||
| 9,7-9,9 | x 1,5 | M10 x 1.5 | 8,2 - 8,6 | ||||
| 10,9-11,1 | 20 GPT | 7/16” - 20 | 9,7 - 10,0 | ||||
| 11,6-11,9 | x 1,5 | M12 x 1.5 | 10,2 - 10,6 | ||||
| 12,4-12,7 | 20 GPT | 1/2” - 20 | 11,3 - 11,6 | ||||
| 12,9-13,1 | 19 GPT | 1/4” | 11,4 - 11,9 | ||||
| 12,9-13,1 | 18 GPT | 1/4” | 11,4 - 11,9 | ||||
| 13,6-13,9 | x 1,5 | M14 x 1.5 | 12,2 - 12,6 | ||||
| 14,0-14,3 | 18 GPT | 9/16” - 18 | 9/16”-18 | 12,7 - 13,1 | |||
| 15,6-15,9 | x 1,5 | M16 x 1.5 | 14,2 - 14,6 | ||||
| 16,3-16,6 | 19 GPT | 3/8” | 14,9 - 15,4 | ||||
| 16,3-16,6 | 18 GPT | 3/8” | 14,9 - 15,4 | ||||
| 17,2-17,4 | 16 GPT | 11/16”-16 | 15,9 - 16,1 | ||||
| 17,6-17,9 | x 1,5 | M18 x 1.5 | 16,2 - 16,6 | ||||
| 18,7-19,0 | 16 GPT | 3/4” - 16 | 17,3 - 17,6 | ||||
| 19,6-19,9 | x 1,5 | M20 x 1.5 | 18,2 - 18,6 | ||||
| 20,4-20,6 | 16 GPT | 13/16-16 | 19,1 - 19,3 | ||||
| 20,5-20,9 | 14 GPT | 1/2″ | 1/2” | 18,6 - 19,0 | |||
| 21,6-21,9 | x 1,5 | M22 x 1.5 | 20,2 - 20,6 | ||||
| 22,0-22,2 | 14 GPT | 7/8” - 14 | 20,2 - 20,5 | ||||
| 22,6-22,9 | 14 GPT | 5/8” | 5/8” | 20,6 - 21,0 | |||
| 23,6-23,9 | x 1,5 | M24 x 1.5 | 22,2 - 22,6 | ||||
| 25,1-25,4 | 14 GPT | 1”-14 | 23,6 - 23,8 | ||||
| 25,6-25,9 | x 1,5 | M26 x 1.5 | 3/4” | 24,2 - 24,6 | |||
| 26,1-26,4 | 14 GPT | 3/4” | 24,1 - 24,5 | ||||
| 26,6-26,9 | 12 GPT | 1 1/16” - 12 | 24,4 - 24,7 | ||||
| 29,6-29,9 | x 2 | M30 x 2 | 27,4 - 27,8 | ||||
| 29,6-29,9 | x 1,5 | M30 x 1.5 | 28,2 - 28,6 | ||||
| 29,8-30,1 | 12 GPT | 1 3/16” - 12 | 27,6 - 27,9 | ||||
| 29,8-30,1 | 12 GPT | 1 3/16”-12 | 28,0 - 28,3 | ||||
| 31,6-31,9 | x 2 | M32 x 2 | 29,4 - 29,9 | ||||
| 33,0-33,2 | 11 GPT | 1” | 30,3 -30,8 | ||||
| 33,0-33,3 | 12 GPT | 1 5/16” - 12 | 30,8 - 31,2 | ||||
| 32,9-33,4 | 11.5 GPT | 1” | 30,3 - 30,8 | ||||
| 35,6-35,9 | x 2 | M36 x 2 | 33,4 - 33,8 | ||||
| 36,2-36,5 | 12 GPT | 1 7/16”-12 | 34,4 - 34,7 | ||||
| 37,6-37,9 | x 1,5 | M38 x 1.5 | 36,2 - 36,6 | ||||
| 40,9-41,2 | 12 GPT | 1 5/8” - 12 | 38,7 - 39,1 | ||||
| 41,6-41,9 | x 2 | M42 x 2 | 39,4 - 39,8 | ||||
| 41,5-41,9 | 11 GPT | 1 1/4” | 39,0 - 39,5 | ||||
| 41,4-42,0 | 11.5 GPT | 1 1/4” | 39,2 - 39,6 | ||||
| 42,5-42,8 | 12 GPT | 1 11/16”-12 | 40,7 - 41,0 | ||||
| 44,6-44,9 | x 2 | M45 x 2 | 42,4 - 42,8 | ||||
| 44,6-44,9 | x 1,5 | M45 x 1.5 | 43,2 - 43,6 | ||||
| 47,3-47,6 | 12 GPT | 1 7/8” - 12 | 45,1 - 45,5 | ||||
| 47,4-47,8 | 11 GPT | 1 1/2” | 44,8 - 45,3 | ||||
| 47,3-47,9 | 11.5 GPT | 1 1/2” | 45,1 - 45,5 | ||||
| 50,5-50,8 | 12 GPT | 2”-12 | 48,7 - 49,0 | ||||
| 51,6-51,9 | x 2 | M52 x 2 | 49,4 - 49,6 | ||||
| 51,6-51,9 | x 1,5 | M52 x 1.5 | 50,2 - 50,6 | ||||
| 59,2-59,6 | 2” | 56,2 - 56,6 | |||||
| 63,1 - 63,4 | 2 1/2” - 12 | 61,1 - 61,4 | |||||
| 65,3 -65,7 | 11 GPT | 2 1/4” | 62,8 - 63,4 | ||||
| 69,1 - 70,9 | 2 1/2” - 8 | 68,5 - 70,2 | |||||
| 74,8-75,2 | 11 GPT | 2 1/2” | 72,2 - 72,9 | ||||
| 81,1 - 81,5 | 11 GPT | 2 3/4” | 78,6 - 79,2 | ||||
| 84,9 - 86,8 | 3” - 8 | 84,3 - 86,1 | |||||
| 87,5 - 87,9 | 11 GPT | 3” | 84,9 - 85,6 | ||||
| 99,9 - 100,3 | 11 GPT | 3 1/2” | 97,3 - 98,0 | ||||
| 112,6 - 113,0 | 11 GPT | 4” | 110,1 - 110,7 | ||||
| Outside diameter | Increase | BSP (T) (K) R | Metric | UNF ORFS | SAIFA (UN thread) | NPTF/NPSM | Inside diameter |
How do you measure a thread?
To identify a thread, you usually need to measure:
- the thread's outer or inner diameter
- the distance between the threads, also known as the pitch
- the number of threads per inch for inch-per-inch threads
- whether the thread is parallel or tapered
Feel free to use a caliper to measure the diameter and a thread gauge to check the thread pitch. Then compare the measurements with the values in the table.
Keep in mind that the measured diameter does not always correspond to the specified inch size of the thread. For example, a 1/2-inch thread does not have an outside diameter of exactly half an inch.
What is the difference between BSP and NPT?
BSP and NPT are two different standards for inch threads.
BSP threads have a thread angle of 55 degrees and are commonly used in Europe and much of the world. NPT threads have a thread angle of 60 degrees and are used primarily in North America.
Although some dimensions may appear similar, the angle, shape, and, in some cases, pitch of the threads differ. BSP and NPT are therefore generally not compatible and should not be screwed together without a suitable adapter.
What is the difference between G-threads and R-threads?
A G thread is a parallel BSP thread, also known as BSPP. The thread diameter remains constant along the entire length of the connection, and sealing is typically achieved using a gasket, O-ring, or sealing surface.
An R-thread is a tapered BSP thread, also known as BSPT. The thread gradually widens, and sealing normally occurs within the threaded joint itself, in conjunction with a suitable thread sealant.
What is the difference between parallel and tapered threads?
A parallel thread has the same diameter along its entire length. It therefore usually requires a separate seal, such as a gasket or O-ring.
A tapered thread varies in diameter along its length. When the connection is tightened, the threads are pressed together, creating a sealing effect.
Can BSP and NPT be used together?
BSP and NPT should not normally be used together. Although they may sometimes begin to thread into each other, their thread angles and thread profiles differ. This can result in a leaky connection, damaged threads, or a connection that cannot withstand the pressure of the application.
Instead, use a transition piece or adapter designed for BSP and NPT.
What does "thread pitch" mean?
Thread pitch refers to the distance between two adjacent thread peaks. For metric threads, the pitch is usually specified in millimeters, for example, M12 × 1.5.
For inch threads, this is often specified as the number of threads per inch, also known as TPI. Two threads with similar diameters may have different pitches and are therefore not compatible.
Do you need help choosing the right threaded component?
The choice of thread type and connection is influenced by factors such as dimensions, pressure, temperature, media, sealing method, and the standard used in the system. We’re happy to help you identify your thread and select the right coupling, adapter, or other component for your application.
Contact us, and we'll help you find the right solution.
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