British Standard Whitworth Thread | BSW Thread Chart

British Standard Whitworth Thread | BSW Thread Chart

  British Standard Whitworth Thread | BSW Thread

The Whitworth thread was the world's first national screw thread standard devised and specified by Joseph Whitworth in 1841. Until then, the only standardization was what little had been done by individual people and companies, with some companies' in-house standards spreading a bit within their industries. Whitworth's new standard specified a 55° thread angle and a thread depth of 0.640327p and a radius of 0.137329p, where p is the pitch. The thread pitch increases with diameter in steps specified on a chart.

The Whitworth thread system was later to be adopted as a British Standard to become British Standard Whitworth (BSW). An example of the use of the Whitworth thread are the Royal Navy's Crimean War gunboats. These are the first instance of mass-production techniques being applied to marine engineering, as the following quotation from the obituary from The Times of 24 January 1887 to Sir Joseph Whitworth (1803–1887) shows

The British Standard Fine (BSF) standard has the same thread angle as the BSW, but has a finer thread pitch and smaller thread depth. This is more like the modern "mechanical" screw and was used for fine machinery and for steel bolts.

The British Standard Cycle (BSC) standard which replaced the Cycle Engineers' Institute (CEI) standard was used on British bicycles and motorcycles. It uses a thread angle of 60° compared to the Whitworth 55° and very fine thread pitches.

  Thread Count (TPI)

TPI stands for Threads Per Inch, Means the total number of threads per inch measured along the length of a fastener. TPI is used only with American fasteners. Metric Fasteners use a thread Pitch. In general, smaller fasteners have finer threads, so the thread count is higher.

  Thread Pitch

Metric fasteners are specified with a thread pitch instead of a thread count. The thread pitch is the distance between threads expressed in millimeters. In general, smaller fasteners have finer thread so they have lower thread pitch.

  BSW Thread Charts

BSW Thread Chart

  British Standard Whitworth Thread Chart | BSW Thread Chart

Nominal Inch TPI Pitch Thread Depth Major Diameter Effective Diameter Minor Diameter Tap Drill Size (mm)
1/8 40 0.025 0.016 0.125 0.109 0.0903 2.55 mm
3/16 24 0.04167 0.0267 0.1875 0.1608 0.1341 3.70 mm
1/4 20 0.05 0.032 0.25 0.218 0.186 5.10 mm
5/16 18 0.05556 0.0356 0.3125 0.2769 0.2413 6.50 mm
3/8 16 0.0625 0.04 0.375 0.335 0.295 7.90 mm
7/16 14 0.07143 0.0457 0.4375 0.3918 0.3461 9.30 mm
1/2 12 0.08333 0.0534 0.5 0.4466 0.3932 10.50 mm
9/16 12 0.08333 0.0534 0.5625 0.5091 0.4557 12.10. mm
5/8 11 0.09091 0.0582 0.625 0.5668 0.5086 13.50 mm
11/16 11 0.09091 0.0582 0.6875 0.6293 0.5711 15.00 mm
3/4 10 0.1 0.064 0.75 0.686 0.622 16.25 mm
7/8 9 0.11111 0.0711 0.875 0.8039 0.7328 19.25 mm
1 8 0.125 0.08 1 0.92 0.84 22.00 mm
1 1/8 7 0.14286 0.0915 1.125 1.0335 0.942 24.75 mm
1 1/4 7 0.14286 0.0915 1.25 1.1585 1.067 28.00 mm
1 1/2 6 0.16667 0.1067 1.5 1.3933 1.2866 33.50 mm
1 3/4 5 0.2 0.1281 1.75 1.6219 1.4938 39.00 mm
2 4.5 0.22222 0.1423 2 1.8577 1.7154 44.50 mm

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