ecause it is often found in the same machinery as the Whitworth standard. However it is actually a <a href="//en.wikipedia.org/wiki/Metric_system" title="Metric system">metric</a> based standard that uses a 47.5° thread angle and has its own set of head sizes. BA threads have diameters of 6&#160;mm (<i>0BA</i>) and smaller, and were and still are particularly used in precision machinery.</p>
<p>The Whitworth 55° angle remains commonly used today worldwide in form of the 15 <a href="//en.wikipedia.org/wiki