The Hosco Fret Levelling File is used after the frets have been installed to level them to each other in preparation for crowning and dressing or for adding a fall away to the high frets. Levelling frets is crucial on a guitar and bass to ensure you can set your desired action without buzzing and it also prevents choking out when bending strings. The file is double sided with single cut teeth on each side, it is for use on standard nickel silver frets (not designed for stainless steel frets).