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[A.S. feol; D. vijl; Ger. feile, allied to Lat. polio, to smooth, and to Gr. phalos, shining.) An instrument used to produce a smooth surface on hard substances, as metals, ivory, wood, . They are made of bars of steel rendered doubly hard by a proce called double conversion, drawn the required size at the tilt hammer, and then shaped. The square and flat ones are formed by the hammer and common anvil only, but the round, half round, and triangular ones are shaped by means of bo es or dies made in the above shapes. The steel blanks are next annealed (see ANNEALING), to render them capable of being cut, by placing a number of them together in a brick oven, rendered air-tight by filling up all the interstices with sand, to prevent oxidation of the steel to which it is liable if air be admitted, and then making a fire play as equally as po ible all round until they are red-hot, when the heat is discontinued and the steel allowed to cool