These are an assortment of files commonly used to sharpen tools. Notice the different shapes ranging from triangular to flat and round. Commonly, the “bastard” is used for sharpening, regardless of shape.
Overlooked frequently in knife sharpening, a file can quickly sharpen many working tools while producing and repairing a keen working edge. Throughout the world, the rudimentary design of the file makes it an indispensable tool to keep around the shop, farm or pack, where there is considerable use of a cutting edge (especially near ground). The file may not produce a super polished edge like an 8,000-grit water stone, but with a little experience one can make a shaving edge in a short period of time.
Abrading instruments have been around for thousands of centuries, and many dwellers of the Stone Age had abrading tools made from fish scales, shark skin, stone, sand and coral. Bronze entered into our history, and more familiar file shapes were seen. Files were made laboriously by hand until around 1735, when machines were created for production. Those made by machine are much better than the handmade files, with teeth at an even angle and depth. Due to the hardness requirement, most files are made out of carbon steel.
The shapes of files vary almost as much as knives do, with triangular files, round files and flat files, to name a few, and preference for use varies by location. Most files come without handles and can be used as is, though stores offer handles and many are improvised—even out of corncobs.