Screws ONLY of the B.A. (British Association) series - typically used in electrical and electronic applications conforming to the appropriate specification and Nickel Plated finishes to BS1224. Other BA parts are in their appropriate main category.
<wiki-snip>They are unusual in that they were probably the most "scientific" design of screw, with a basis in metric size (the 1 mm pitch and 6 mm diameter of 0BA) and with a mathematical relationship between the 'number' (e.g. 2BA with K=2) and the corresponding pitch, major diameter, and then spanner size. Though originally defined in terms of the imperial units then in use in the United Kingdom, this was deliberately set to be exact multiples of the metric system units, rounded to the nearest thousandth of an inch. This anticipated worldwide metrication by about a century. The design was first formulated in 1884, following a study of Swiss practice and was standardised in 1903.<snip>