This free thread size chart from HAGUE FASTENERS LIMITED gives the pitch, diameters, stress area and tapping drill for ISO metric coarse and fine, UNC, 8UN and UNF, BSW and BSF Whitworth, BA and BSP pipe threads.
Not sure what thread you have? Switch to the thread identifier, enter the measured diameter and pitch, and it lists the closest matches across every system.
Thread data and thread identifier
Tolerance limits from the ISO 965-1 tables for metric threads and ASME B1.1 for unified threads. Basic dimensions from the thread form of each standard. Tensile stress area for unified threads from ASME B1.1, for metric from ISO 898-1, and for Whitworth, BA and BSP from the mean of pitch and minor diameters.
Guidance only. Results are approximate and for initial guidance. They are not a substitute for the governing standard, specification or drawing, or for testing. HAGUE FASTENERS LIMITED accepts no liability for decisions made using these tools. Always check critical values against the relevant standard. © 2026 HAGUE FASTENERS LIMITED.
How to use the thread size chart
- To look up a thread, choose the size from the list. Sizes are grouped by thread system.
- To identify an unknown thread, choose “Identify a thread from measurements”, then enter the outside diameter measured with calipers and the pitch from a thread gauge, in mm or threads per inch.
- Check the thread angle with a gauge to tell 55 degree Whitworth and BSP threads from 60 degree metric and unified threads, which can measure almost the same.
Frequently asked questions
What is the difference between BSW and UNC?
Whitworth threads have a 55 degree thread angle with rounded crests and roots, while unified threads such as UNC have a 60 degree angle. Some sizes also have a different pitch: 1/2″ BSW has 12 threads per inch and 1/2″ UNC has 13. The two are not interchangeable, even where the pitch is the same.
What is the tensile stress area?
It is the effective area of a threaded part used to work out its strength, such as the load at yield or proof load. It lies between the pitch and minor diameter areas. Our bolt torque calculator uses it to work out preload.
Can you make old British or non-standard threads?
Yes. HAGUE FASTENERS LIMITED makes special fasteners to drawing or sample, including Whitworth, BSF and BA threads, and non-standard sizes and pitches. Send us your drawing or sample details.
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Need special fasteners made to drawing, sample or specification? Send us an enquiry or call +44 (0)1902 365 865.