A guide to different Thread Types

Metric Coarse
The most common thread type coarse threads are larger in pitch than fine threads (there are fewer threads along the distance of the thread).

Metric fine
Another common thread, more threads along the distance of the thread than coarse thread.

BSW (British Standard Whitworth) & BSF (British Standard Fine)
BSW is an Imperial coarse thread standard established in 1841. Whilst it is still used across the world it is less common than metric threads which have generally taken over. BSF is the fine-pitch alternative it is commonly used in engineering and automotive applications in the UK.

UNF (Unified National Fine) & UNC (Unified National Coarse)
Unified thread types were introduced during World War 2 to facilitate international interchangeability of machinery manufacturing. Still commonly found on old machines and vehicles in the UK.

BSP (British Standard Pipe)
Used in the UK and internationally as a standard thread for the plumbing and pipe fitting industry.

BA (British Association)
A specialized screw thread system designed for small precision fasteners. Although rarer now due to being replaced with ISO standards, it was once commonly found on small instruments and models and is still used in some industries.

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