British Army marked spanners are one of the most common tools to come across in boxes of old tools and I make a point of always hunting through to see what I can find. Over the years I have collected up quite a few of these humble tools and rarely paid more than 50p each for them. World War II spanners come either marked ‘BSW’ and ‘BSF’ like these:

Or marked ‘AF’ and ‘W’ like these:

These letters refer to the most common thread types in use in Great Britain at the time, before the widespread adoption of metric or the size of the nuts. A/F means ‘across the flats’ and measures the bolt head. BSF is British Standard Fine, W is Whitworth and BSW is British Standard Whitworth. Whitworth was the first standardised thread measurement and was adopted in the 1840s. The standardisation of thread sizes was to be a great boon to the military, as indicated by this account from the Crimean War:

The Crimean War began, and Sir Charles Napier demanded of the Admiralty 120 gunboats, each with engines of 60 horsepower, for the campaign of 1855 in the Baltic. There were just ninety days in which to meet this requisition, and, short as the time was, the building of the gunboats presented no difficulty. It was otherwise however with the engines, and the Admiralty were in despair. Suddenly, by a flash of the mechanical genius which was inherent in him, the late Mr John Penn solved the difficulty, and solved it quite easily. He had a pair of engines on hand of the exact size. He took them to pieces and he distributed the parts among the best machine shops in the country, telling each to make ninety sets exactly in all respects to the sample. The orders were executed with unfailing regularity, and he actually completed ninety sets of engines of 60 horsepower in ninety days – a feat which made the great Continental Powers stare with wonder, and which was possible only because the Whitworth standards of measurement and of accuracy and finish were by that time thoroughly recognised and established throughout the country.

These spanners are much later in date, but the standards remained the same. Each spanner is marked with the /|\ property mark, and usually the date in a variety of styles:

Trying to build up a full set of spanners to a thread size and manufacturer would be difficult but not impossible and there is a certain thrill in hunting through boxes of junk to find marked tools to rescue for the collection!