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.