Have you ever wondered why understanding thread pitch and tooth count is crucial in mechanical engineering? These parameters are key in defining the characteristics and performance of threaded fasteners. This article explains the differences between Whitworth and Unified Standard threads, providing essential tables and charts for reference. By the end, you’ll grasp how to select the right thread type for your projects, ensuring precision and reliability in your mechanical designs.
Inch threads include Whitworth threads and Unified Standard threads.
Whitworth threads are the standard threads used for British inch fasteners, with a thread angle of 55 degrees. They are typically represented by the nominal diameter (in inches) and the number of threads per inch, using the symbol “”. For example, 1/2″-12BSW represents a coarse Whitworth thread with a nominal diameter of 1/2 inch.
Unified Standard threads are the standard threads used for American inch fasteners, with a thread angle of 60 degrees. They are generally represented by a code (for nominal diameters less than 1/4 inch) or the fraction of the nominal diameter in inches (for those greater or equal to 1/4 inch), the number of threads per inch, and a designation (UNC, UNF). For example, 1/2″-13UNC represents a coarse Unified Standard thread with a nominal diameter of 1/2 inch.
Nominal diameters and threads per inch of Whitworth threads and Unified Standard threads:
| Major Thread Diameter | Unified Standard Thread ANSI B1.1-182 | Whitworth Thread BS84-1956 | ||||
| Inch | Size Code | Coarse Thread UNC | Fine Thread UNF | Size Code | Coarse Thread BSW | Fine Thread BSF |
| 0.0600 | 0# | 80 | ||||
| 0.0625 | 1/16 | 60 | ||||
| 0.0730 | 1# | 64 | 72 | |||
| 0.0860 | 2# | 56 | 64 | |||
| 0.0938 | 3/32 | 48 | ||||
| 0.0990 | 3# | 48 | 56 | |||
| 0.1120 | 4# | 40 | 48 | |||
| 0.1250 | 5# | 40 | 44 | 1/8 | 40 | |
| 0.1380 | 6# | 32 | 40 | |||
| 0.1563 | 5/32 | 32 | ||||
| 0.1640 | 8# | 32 | 36 | |||
| 0.1875 | 3/16 | 24 | 32 | |||
| 0.1900 | 10# | 24 | 32 | |||
| 0.2160 | 12# | 24 | 28 | |||
| 0.2189 | 7/32 | 24 | 28 | |||
| 0.2500 | 1/4 | 20 | 28 | 1/4 | 20 | 26 |
| 0.2812 | 9/32 | 26 | ||||
| 0.3125 | 5/16 | 18 | 24 | 5/16 | 18 | 22 |
| 0.3750 | 3/8 | 16 | 24 | 3/8 | 16 | 20 |
| 0.4375 | 7/16 | 14 | 20 | 7/16 | 14 | 18 |
| 0.5000 | 1/2 | 13 | 20 | 1/2 | 12 | 16 |
| 0.5625 | 9/16 | 12 | 18 | 9/16 | 12 | 16 |
| 0.6250 | 5/8 | 11 | 18 | 5/8 | 11 | 14 |
| 0.6875 | 11/16 | 11 | 14 | |||
| 0.7500 | 3/4 | 10 | 16 | 3/4 | 10 | 12 |
| 0.8125 | 13/16 | 12 | ||||
| 0.8750 | 7/8 | 9 | 14 | 7/8 | 9 | 11 |
| 1.0000 | 1 | 8 | 12 | 1 | 8 | 10 |
| 1.1250 | 1-1/8 | 7 | 12 | 1-1/8 | 7 | 9 |
| 1.2500 | 1-1/4 | 7 | 12 | 1-1/4 | 7 | 9 |
| 1.3750 | 1-3/8 | 6 | 12 | 1-3/8 | 8 | |
| 1.5000 | 1-1/2 | 6 | 12 | 1-1/2 | 6 | 8 |
| 1.6250 | 1-5/8 | 1-5/8 | 8 | |||
| 1.7500 | 1-3/4 | 5 | 1-3/4 | 5 | 7 | |
| 2.0000 | 2 | 4.5 | 2 | 4.5 | 7 | |
| 2.2500 | 2-1/4 | 4.5 | ||||
| 2.5000 | 2-1/2 | 4 | ||||
| 2.7500 | 2-3/4 | 4 | ||||
| 3.0000 | 3 | 4 | ||||
| 3.2500 | 3-1/4 | 4 | ||||
| 3.5000 | 3-1/2 | 4 | ||||
| 3.7500 | 3-3/4 | 4 | ||||
| 4.0000 | 4 | 4 | ||||
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