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British Standard Fine (BSF) is a screw thread form, as a fine-pitch alternative to British Standard Whitworth (BSW) thread. It was used for steel bolts and nuts on and in much of Britain's machinery, including cars, prior to adoption of Unified , and later Metric , standards.
A screw thread is an inclined plane wrapped around a cylinder or cone in the form of a helix, with the former being called a straight thread and the latter called a tapered thread. More screw threads are produced each year than any other machine element. [1] Threads are generally produced according to one of the many standards of thread systems.
British Standard Whitworth (BSW) is an imperial-unit-based screw thread standard, devised and specified by Joseph Whitworth in 1841 and later adopted as a British Standard. It was the world's first national screw thread standard, and is the basis for many other standards, such as BSF , BSP , BSCon , and BSCopper .
Taper threads, British Standard Pipe Taper thread (BSPT), whose diameter increases or decreases along the length of the thread; denoted by the letter R. BSPT threads [2] These can be combined into two types of joints: Jointing threads These are pipe threads where pressure-tightness is made through the mating of two threads together.
The common V-thread standards (ISO 261 and Unified Thread Standard) include a coarse pitch and a fine pitch for each major diameter. For example, 1 ⁄ 2 -13 belongs to the UNC series (Unified National Coarse) and 1 ⁄ 2 -20 belongs to the UNF series (Unified National Fine).
This was simplified in the BA thread definition by defining the thread angle to be 47.5° exactly and the thread form to be symmetrical with a depth of 3 / 5 p. The British Standards Institution recommends the use of BA sizes in favour of the smaller British Standard Whitworth (BSW) and British Standard Fine (BSF) thread screws (those ...
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Example (inch, fine): For 7 ⁄ 16-20 (same diameter as the previous example, but this time with 20 threads per inch, which is considered fine), 0.437 in × 0.90 = 0.393 in (i.e., if the threads are to be fine, then a slightly larger diameter drill bit should be used before tapping the hole for the screw).