Terminology
There are thousands of pages on the Internet that describe the terminology of fasteners. Ours is slightly different. It does not try to list everything, it describes old terminology and not the new, and limited to the often unknown or terms that are often confused.
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Black Nuts and Bolts
Black nuts and bolts are often described as those that a blacksmith would have produced but this definition is not complete. Steel for fasteners used to be produced by red hot metal being shaped by rolling it into smaller shapes and then drawing it through a shaped cold steel former. As the metal then cooled it oxidised giving it a blackened look. This is black steel from which black nuts and bolts, or washers, etc are formed.
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A strip of black steel 1/4” thick and 1/2” wide can be easily drilled and cut to make a square nut. A hex nut drilled and easily parted from a hex bar. Both will still have large areas of oxidised black on them. The fasteners that were made by hand in the forge were later made by machine, the production speed increasing but the product very similar with oxidised layers still present with the name remaining the same.
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Black nuts and bolts are not to be confused with self-coloured nuts and bolts even though the same oxidised layer exists.
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Black Steel
Steel that has been heated to red hot and cooled leaving an oxidised layer on the outside.
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Bright Nuts and Bolts
As material science improved so did metal, and in turn the tools and machinery. Steel could be made stronger, harder, tolerances finer and quality controlled. Stronger, faster machinery replaced manpower, the production line improved, standard sizes within tolerance created by machine to be fitted by machine.
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The black bar of before was often outside tolerance needed so they were drawn through a former when the metal was cold to the tolerance needed. This had the effect of removing most of the oxidisation giving a brighter appearance. The further pressing, cutting and machining to reach the fine tolerance also produced bright surfaces, hence bright nuts, bolts and washers.
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Bright Steel
Steel that has been formed or processed by rolling, drawing milling, turning, etc to leave a brighter surface than black steel.
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Cycle Engineers' Institute (CEI)
This is a thread for used bolts, nuts, nipples, spokes, and other threaded parts of cycles and motorcycles. It was standardised by the CEI in 1902 and became a British Standard in 1938 with BS811. The thread was known as CEI or Cycle up to 1938 and from then it has been known as BSCy, BSc, Cycle or officially as BSC.
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It is a thread that is very similar to the Whitworth forms of threads but has a 60° flank angle, but they are not interchangeable. Whilst some nuts or bolts between the different thread forms seem to fit with a bit of extra force, this will lead to the fastener failing over time.
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The original CEI thread sizes were related to the size of the wire or bar rather than being derived by a mathematical formula. A diameter wire was provided, and the committee seemed to give it a TPI based on their opinion or took the opinion of the manufacturer that presented the sample. The 1938 standard did not recognise all the possible threads and by 1950 when the standard was re-issued only the popular sizes were kept.
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A design drawing often used any of the short name forms from above to show that cycle thread was needed and not Whitworth or Fine. A common form for use on drawings was simply 26 TPI where the fastener was between 1/4" and 1" as those fasteners all had the same TPI. The TPI of the range of the CEI thread ran from 56TPI to 24TPI across a diameter range from 0.072” to 1 5/8”.
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CEI20
There is also a Cycle Engineers' Institute thread named CEI 20TPI. It is a thread form that is based on the Whitworth 55° flank angle rather than the 60° flank angle form. This thread form covers diameters from 7/16” to 3/4” and they all use the same 20TPI. Unlike the fasteners with 26TPI, there are no thread form clashes between CEI20, BSW and BSF. CEI20 is defined in the 1938 British Standard for BSC.
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Half Nuts
The name is derived from the lock nut which itself has disappeared over time and been replaced by other fastenings such as nyloc, Stover, Philidas, etc and chemical thread locking compounds. The last British Standard in 1965 for BSW and BSF defined the height of a lock nut to be 2/3rds of that of the ordinary nut. Some manufacturers produce these literally at 1/2 the height of a nut rather than 2/3rds.
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Hexagon
Used to describe both the shape of the head of a bolt or a nut, and the type of bolt or nut. An alternative type could be a square for example.
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Light Nuts
At the beginning of the 20th century there were thinner nuts that were called light nuts. These were reduced to 2/3rds of the height of a standard nut. These light nuts were used as a lock nut and over time the phrase light nut disappeared from use.
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Lock Nuts
Simply a nut tightened on top of another nut. Its job was not to keep the fastened items together or to increase the force to hold things together but to help stop the vibration from undoing the main nut. As the lock nut was not tightened to the same force as the main nut, it could be thinner. It was also a good indicator of a problem to come. It was easy to see when the lock nut was loose or missing.
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Castle Nuts replaced many lock nuts and in turn were replaced by mechanical self-locking fasteners such as nyloc, Stover, Philidas, and also chemical thread locking compounds. The aerospace and racing industries also use safety wire locked nuts to keep the weight down.
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But the day of the lock nut has passed, and these are now known as half nuts.
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Self-Coloured
This term relates to a fastener that has been heat treated to strengthen the steel. The heating process creates a black layer of oxidisation. They are not called back fasteners as that would confuse them with black nuts and bolts or washers, etc.
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