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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).
Unified Screw Threads with Tolerances; Unified Coarse/Fine diameters and tap drill sizes (U.S. units) Unified Coarse/Fine tap drill sizes (U.S. units) Imperial Metric fastening size conversion charts; International Thread Standards; Conversion chart Whitworth/BSF/AF and metric Archived 2 May 2010 at the Wayback Machine
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). Similarly, M10 (10 mm nominal outer diameter) as per ISO 261 has a ...
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.
The terms coarse and fine have (in this context) no relation to the manufacturing quality of the thread. In addition to coarse and fine threads, there is another division of extra fine, or superfine threads, with a very fine pitch thread. Superfine pitch metric threads are occasionally used in automotive components, such as suspension struts ...
V Thread Form BS 84: Tables of BS Whitworth, BS Fine and BS Pipe Threads: V Thread Form (55°) 1 ⁄ 4 ″-20 BSW ISO 68-1:1998: ISO general purpose screw threads—Basic profile—Part 1: Metric screw threads: V Thread Form ISO 68-2:1998: ISO general-purpose screw threads—Basic profile—Part 2: Inch screw threads: V Thread Form ISO 261:1998
The major minus pitch technique also works for inch-based threads, but you must first calculate the pitch by converting the fraction of threads-per-inch (TPI) into a decimal. For example, a screw with a pitch of 1/20 in (20 threads per inch) has a pitch of 0.050 in and a 1 ⁄ 13 in pitch (13 threads per inch) has a pitch of 0.077 in.
The thread angle is different from that used by Whitworth (55°), US Unified threads (60°) and ISO Metric (60°) so BA fasteners are not properly interchangeable with Whitworth or metric ones even when the pitch and diameter are similar enough that they can be screwed together (e.g., although 0BA appears similar to M6×1mm, the male and female ...