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2024.1.11
When you are using a fastener, thread pitch is a frequently used term, and it determines whether two parts properly fit each other. In this post, we want to concentrate on thread pitch, covering its definition, types, reading, measurement, as well as metric and American thread pitch chart.
The thread pitch is defined as the distance between the same point on adjacent threads of a fastener, it is one of the key parameters to describe the thread size or dimension. For example, a 1/4″-20 thread means its diameter is 1/4” and threads per inch is 20.
If you are wondering does a bolt thread into a mating nut or threaded hole, you need to know its pitch. You can change parts with the same thread pitches.
How do you measure the thread pitch?
The pitch of a thread is measured parallel to the axis. To measure the pitch, you can use a caliper to check the distance between crests of two threads, you can also get the result through calculation, as long as you know the entire length of the thread and the number of threads. To read thread pitch, measure the distance between corresponding points on adjacent threads. It can also usually be found printed or stamped on the fastener.
What is the most common thread pitch?
The most common imperial thread pitches are 1/4″-20, 5/16″-18, 3/8″-16, and 1/2″-13. The most common metric thread pitch is 1 mm or 1.5 mm.
There are different types of thread pitches, including coarse, fine, extra-fine, special/extra-special, etc.
– Coarse Thread Pitch: Coarse threads have a relatively large distance between threads. This makes for fewer threads per inch/centimeter.
– Fine Thread Pitch: Fine threads have a smaller distance between threads, resulting in more threads per inch/centimeter.
– Extra Fine Thread Pitch: Even finer than fine threads, with pitches measured in fractions of an inch rather than whole numbers. Often used in applications requiring an exceptionally close-tolerance thread interface, such as optics equipment.
– Special/Extra Special Thread Pitch: Along with tighter tolerances, special and extra-special threads have finer pitches than standard thread classes. They provide a very close-fitting thread for high-precision uses like aerospace components.
– Metric Thread Pitch: Metric threads are designated in millimeters such as 0.5mm, 0.7mm, 1mm or 2mm pitch. 1mm is a common general-purpose pitch while coarser 2mm is also widely used.
– Unified Thread Pitch: UNC for coarse threads and UNF for fine threads having set the major diameter to pitch pairings, ensuring interchangeability.
– Custom Thread Pitch: A non-standard pitch can be specified for unique assembly needs not met by existing thread types and sizes.
Coarse vs Fine Thread, What Are the Differences?
Coarse threads have a larger pitch than fine threads, the coarse pitches are stronger, while the fine pitches offer a closer fit between threads, which improves the friction for clamping force and sealing, so the fine threads are not easy to be loosen.
In metric standards, M10-1.50 is a coarse thread denotation while M10-1.25 is a fine pitch. In American standard, 1/4”-20 is a coarse thread (UNC) and 1/4”-28 is a fine thread (UNF).
Below you can check out the Metric and American thread pitch charts.
Metric Thread Pitch Chart
American Thread Pitch Chart
| Size | Coarse | Fine | Extra Fine |
|---|---|---|---|
| M1 | 0.25 | – | – |
| M1.6 | 0.35 | – | – |
| M2 | 0.40 | – | – |
| M2.5 | 0.45 | – | – |
| M3 | 0.50 | – | – |
| M3 | 0.35 | – | – |
| M3.5 | 0.60 | – | – |
| M4 | 0.70 | – | – |
| M5 | 0.80 | – | – |
| M6 | 1.00 | – | – |
| M7 | 1.00 | – | – |
| M8 | 1.25 | 1.00 | – |
| M10 | 1.50 | 1.25 | 1.00 |
| M12 | 1.75 | 1.50 | 1.25 |
| M14 | 2.00 | 1.50 | – |
| M16 | 2.00 | 1.50 | – |
| M18 | 2.50 | 1.50 | – |
| M20 | 2.50 | 1.50 | – |
| M22 | 2.50 | 1.50 | – |
| M24 | 3.00 | 2.00 | 1.50 |
| M27 | 3.00 | 2.00 | – |
| M30 | 3.50 | 2.00 | – |
| M33 | 3.50 | 2.00 | – |
| M36 | 4.00 | 3.00 | – |
| M39 | 4.00 | 3.00 | – |
| M42 | 4.50 | – | – |
| M45 | 4.50 | – | – |
| M48 | 5.00 | – | – |
| M52 | 5.00 | – | – |
| M56 | 5.50 | – | – |
| M60 | 5.50 | – | – |
| M64 | 6.00 | – | – |
| M72 | 6.00 | – | – |
| M80 | 6.00 | – | – |
| M90 | 6.00 | – | – |
| M100 | 6.00 | – | – |
| Size | UNC | UNF |
|---|---|---|
| #0 | – | 80 |
| #1 | 64 | 72 |
| #2 | 56 | 64 |
| #3 | 48 | 56 |
| #4 | 40 | 48 |
| #5 | 40 | 44 |
| #6 | 32 | 40 |
| #8 | 32 | 36 |
| #10 | 24 | 32 |
| #12 | 24 | 28 |
| #1/4″ | 20 | 28 |
| 3/8″ | 16 | 24 |
| 7/16″ | 14 | 20 |
| 1/2″ | 13 | 20 |
| 9/16″ | 12 | 18 |
| 5/8″ | 11 | 18 |
| 3/4″ | 10 | 16 |
| 7/8″ | 9 | 14 |
| 1″ | 8 | 14/12 |
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