Whilst the most common War Department marked tools that turn up are spanners, for Air Ministry marked tools, measuring devices seem to be some of the easier items to find. A few weeks back I was lucky enough to find a pair of Air Ministry marked callipers in a tool box and for the princely sum of £2 they were mine:Callipers are mainly used for measuring the diameter of cylinders, although have other uses in light engineering work. This pair have a crown and AM marking on one of the legs, together with a maker’s name of Buck and Hickman Ltd:Interestingly they also bear a /|\ mark and an inspector’s code 60 on the reverse:Using callipers correctly requires a little practice and a 1930s engineering manual gives this advice:

Measuring with Callipers

Callipers, either spring or firm joint types, are convenient tools for measuring a number of jobs which are not required to be extremely accurate. Firm joint callipers have two legs fastened together with a rivet or bolt of a special design. To give a smooth joint thin fibre-washers are interposed between the legs, and when purchasing callipers this point should be looked for.

The legs of inside callipers are curved outward at the extremities to facilitate measuring small holes, whilst outside calliper legs have a large curve inward to increase their capacity for large work.

Firm joint callipers are adjusted approximately by the hands and then set to the “feel” of the work by tapping them on a metal surface. It is common practice when opening callipers by this means to tap the top of the joint. It is better, if possible, to tap the inside of the legs, as repeated blows, though light, tend to burr the edges of the joint. Care should be taken when using callipers to hold them square across the job, or an incorrect reading will be obtained. The interference between the work and the instrument should be very slight as distortion of the legs occurs if force is used. The application of callipers for good results calls for a certain amount of practice.

The book also illustrates another use for this instrument:

Feeler gauges are used to check the clearances of fittings within precision machines such as engines. A set of feeler gauges consist of a set of different metal fingers, each of a different width. Each finger is marked with its thickness, and by trying each in turn, or a combination of different ones, the correct clearance can be set. These have been in service for many decades and tonight we have an Air Ministry marked set dating back to 1939. Folded up the feeler gauge is just a small metal bar:A cut-out is provided on one side that allows the gauges to be pushed out from their housing:Fanned out it can be seen that a wide range of thicknesses are housed in the tool:Each gauge has its thickness in thousandths of an inch etched into its surface:These gauges go from 3/1000″ up to 15/1000″ and the gauges are flexible enough that multiples can be held together to make up different thicknesses.

The gauge itself has a crown and AM stamp along with a date of 1939 indicating it was produced for the RAF:This tool was manufactured by Moore and Wright of Sheffield. The company is now part of the Bowers group, and their website gives some history:

Founded in 1906 by innovative young engineer Frank Moore, Moore & Wright has been designing, manufacturing and supplying precision measuring equipment to global industry for over 100 years. With roots fixed firmly in Sheffield, England, the company began by manufacturing a range of callipers, screwdrivers, punches and other engineer’s tools.

The uses for feeler gauges included setting the tappet valves in engines, as explained in a 1953 army handbook on basic mechanical principles for tracked and wheeled vehicles:

Clearance between the valve stem and tappet is tested with a feeler gauge. If the appropriate feeler just pushes through the gap with little force the setting is correct. To make certain try the next size up, this should not go.

Steel rules are essential measuring devices in any workshop. The properties of metal allow a worker to score along the edge of the ruler without any fear of damaging the rule itself, a common problem with wood or plastic rulers. Metal rules have been used for the marking out of sheet metal for many centuries and it is therefore unsurprising that examples exist that are marked up to show they belong to the military. The RAF especially relied on fitters and mechanics to keep aircraft serviceable, right form its inception. These men needed extensive tool kits and amongst these would be a steel rule. Tonight we have an Air Ministry marked example to look at:This 6” rule is stamped with the crown and AM mark of the Air Ministry and has a date of 1939:Dating from the 1930s, this rule is predominantly set up to measure fractions of an inch, however the reverse does have a metric scale as well:The use of a steel rule was viewed as so important that the US actually produced a thirteen minute training film on its use for metal workers! This film can be seen here.

The role of the aircraft fitter was essential to repair aeroplanes and get them back into the sky. John Morris served as a groundsman in World War Two:

Each transport took us to the aerodrome which was about 5 miles from Setif, it was the French Air force and had one or two hangars in which to work on the aircraft. Aircraft were brought to the unit when they had flown a large number of hours, which was called a major inspection. They would be jacked up on large metal jacks in what was known as rigging or flying position, the engines were removed, petrol tanks dropped, hydraulics checked, metal replaced with rivets between the engine nacelle and the fuselage where heavy boots walked over the wing when re-fuelling, the metal got stretched. When all of this had been done, the aircraft was re-sprayed, placed in a pool ready for the next squadron that required a replacement aircraft. It was mainly Bristol Beaufighters that were worked on. A twin-engine, two crewed night fighter, fitted with radar, later used for anti-shipping. It was also converted to carry a torpedo or eight 60 lb. rockets.

One repair job I shall always remember was a Beaufighter that had been built with countersinking too large and the rivets sunk below the level of the outside skin. Two of us replaced a thousand oversize rivets making the fuselage smooth. Later it was mentioned that this aircraft had gone out with other planes from the squadron and pumped 55 rockets into the Rex, a 55,000 ton Italian liner just below the water line and sinking the ship just off Trieste.