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Spanners, Sockets and Wrenches.
History and Development 

In the latter part of the 1700s, lead by the UK, the world's manual labour-based economies began to change into one dominated by industry and the manufacture of machinery.

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Trade expansion was enabled by the introduction of canals, improved roads and railways, steam power and powered machinery contributing to the dramatic increases in industrial production.

So, there was a massive explosion in the production of machinery, vehicles and equipment, all requiring screws nuts and bolts to hold them together.

Needless to say, there grew a huge need for tools for tightening and loosening the various screw fastening systems that were developed.

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But like all early developments, differing countries adopted different standards. Partly it was for competitive reasons and partly through technical reasons.

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This gave rise to the huge range of differing screw thread forms and the different sized nuts and bolts that were being used. The following gives you some idea:

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Unified Thread Standard (UTS) which is still in common use in the United States and Canada. This standard includes:

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  • Unified Coarse (UNC)

  • Unified Fine (UNF)

  • Unified Extra Fine (UNEF)

  • Unified Special (UNS)

  • National pipe thread (NPT)

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British Standard Whitworth (BSW), and other Whitworth threads including:

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  • British Standard Fine (BSF)

  • Cycle Engineers' Institute (CEI)

  • British standard pipe thread (BSP)

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British Association screw threads (BA)

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Besides the fact that none of these are interchangeable, all have nuts and bolts with different sizes!

Clearly this couldn’t go on as companies were finding that pieces of equipment were incompatible, or they didn’t have the right maintenance tools (a big problem during World War II).

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So the International Organization for Standardization (ISO) was founded in 1947 and in 1960 it published a new standard covering metric screws and BSP pipe threads.

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Largely, the ISO standard has been adopted worldwide (but not completely in the USA) meaning that having a set of Metric spanners or sockets will get you a long way in most jobs.

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So let’s get some terminology out of the way before we have a look at the tools in more details...

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