Metrication in The United Kingdom - 1965 Onwards - Metrication of Engineering-related Industries

Metrication of Engineering-related Industries

There was no single approach to the metrication of the engineering industry: in some areas soft metrication was applied and in others hard metrication. In certain branches metrication was achieved by adopting the equivalent European or international standard, but this was not always possible as certain standards, such as BS 1363 which defined electric plugs were peculiarly British while the petrochemical industry had standardised on API and ANSI standards.

An example of a hard metrication changeover was the threaded fastener industry (nuts and bolts) where 21 "first choice" BSW, BSF and BA series thread in the range 0 BA to 1 inch plus another 20 UNC and UNF fasteners were replaced by just seven metric sizes. This resulted in considerable cost savings, not only due to the reduction in inventories, but also the numbers of taps, dies, tapping and clearance drills that workshops held.

As example of soft conversion was the construction products industry (metricated 1969 and 1972) where certain products continue to be produced to with reference to Imperial trade names but made using metric dimensions in the factory; for example, a 13 mm thick plasterboard is still often called 'half-inch', even though the measurement is rounded to a convenient metric size and so is now only approximately half an inch thick. The construction industry itself (which included civil engineering projects) was one of the leaders in the metrication programme, having drawn up a detailed plan in 1967 and completing the phase-over by the end 1972.

The BSI, after consultations with the engineering industry, had set a target of 75% of the industry being metric by the end of 1975. This target was not reached, one of the principal reasons being that other sectors, especially the retail sector, were lagging in reaching their targets.