[Ferguson]

What Lew said is correct. Probably made from a rasp, which has large coarse teeth made for cutting soft material like wood.

Files and rasps come in all sizes, some fairly large. As the blade is forged down to a thin edge, it gets wider, and retains the pattern of the teeth.

Files are hard and brittle because of the heat treatment. They are made that way to cut steel. Brittleness is not an issue because there is no impact involved. Further tempering (heating at a low temp, maybe 350 fareinheit) reduces hardness and increases toughness, which is what you want for a knife blade.

This gile was forged from a file, or rasp.

Edit:
A file that is .25" thick by 1.5" wide has a cross sectional area of .375 square inches.
A diamond shaped blade .1875" thick at the center, 3" wide has a cross sectional area of only .2813 square inches.
So it's easy to see that a rectangular file could be forged into a fairly wide diamond sectioned blade.


Steve