The Elmer Guitar Offset Double Edged Diamond Fret Crowning File has two different sized concave edges for dressing frets after levelling, one side is for narrow to medium fretwire and the other is wider for medium to jumbo fretwire and the curved offset ends allow the file to be used more easily on the heel end frets over the guitar body. The filing grooves are coated with graded diamond particles for chatter free use in both directions giving great control and you have a choice of 150 or 300 grit files, 150 grit is an aggressive cut for removing a lot of material quickly and 300 grit is smoother for more general use.