Made in Japan by a company that has been manufacturing files for 80 years and guitar files for three decades, these are the best on the market for sharpness, regularity of cut and durability.
Cutting string slots with a saw and rounding them with a needle file can be a painstaking, time-consuming process. These files let you cut and shape the slot in a single operation. They have fine single-cut teeth on both edges, with the faces left smooth to avoid widening the slot. The rounded edges shape the bottom of the slot as you cut it to match the curvature of the string.
Sized to match diameters of the most common acoustic and classical guitar strings, they are available individually. Each is 6" overall with a 4 1/2" cut length.