Non-metric Screws
Before the metric system was common, many engineering companies had their own standard screw sizes. The first person to create a standard (in about 1841) was the English engineer Sir Joseph Whitworth. Whitworth screw sizes are still used, both for repairing old machinery and where a coarser thread than the metric fastener thread is required. This system had two thread sizes: coarse (BSW) and fine (BSF). The thread angle was 55°.
A later standard in the UK was the BA system, named after the British Association for Advancement of Science. Screws were described as "2BA", "4BA" etc., the odd numbers being rarely used. While not related to ISO metric screws, the sizes were actually defined in metric terms, a 0BA thread having a 1mm pitch. These are still the most common threads in some niche applications. Certain types of fine machinery, such as moving-coil meters, tend to have BA threads wherever they are manufactured.
The USA has its own system, usally called SAE, for Society of Automotive Engineers. Screws are described as 4-40, 6-32, 8-32, 10-32, 10-24, etc. (for numeric sizes, odd numbers are rare), or 1/4"-20, 1/4"-28, etc. (for inch unit sizes), with the first number giving shaft diameter (numeric or inches) and the second number being threads per inch. These screws are sometimes found outside the USA in personal computers based on the IBM PC specification. There must be millions of PCs outside the USA that have metric screws jammed into non-metric holes!
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Modern-day powered ships and boats are nearly always driven by screw propellers, often referred to as the "ship's screws". In the early days of steam power for ships, when both paddle wheels and screws were in use, ships were often characterized by their type of propellers, leading to terms like screw steamer or screw sloop.
Also see Archimedes' screw for a type of pump containing a screw as its impeller.