You can use this RS PRO thread pitch gauge to identify the pitch of your screw threads. It consists of a penknife-style handle, with 27 separate blades. These have pitches that range from 4 per inch to 56 per inch, which should provide enough range to cover your needs.
The blades are organised into two groups at either end of the tool, with a screwable locking device that can be used to hold them in place. This allows for better stability when you're carrying out measurements, improving the accuracy of your work. You can also use it to secure the blades when they're retracted, ensuring safe storage and transportation.
The product is designed to suit Unified, American National and Whitworth thread profiles. It's an ideal tool for use in workshops and industrial manufacturing environments.

• 27 blades
• Sizes include 4, 4-1/2, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 16, 18, 19, 20, 22, 24, 25, 26, 28, 30, 32, 36, 40, 48, 60
• Imperial thread type
• Imperial measure range of 4 threads per inch (TPI) to 60 TPI
• Metric measure range of 4 mm to 60 mm