The Hosco Ultimate Fret Crown Optimizer 1 was born out of the desire to develop a product that allows maximum precision when crowning frets. Most of the files on the market do not cover all the radii and depths that a luthier can come across. The Hosco UFO 1 solves this problem with 4 radii per model that allow you to find the exact radius you need for your fret. In addition, the small size is very easy on the hand. The file faces are coated with 600 grit diamond powder. Made in Japan.