Which instruments can it works on? Three gauges slot are provided in 1mm,2mm,3mm, That means it'll works on most stringed instruments frets. The 1mm slot works for extra narrow frets, likes ukuleles. The 2mm slot works for all standard guitars, bass, banjo, mandolin, cigar box guitars. The 3mm slot works for jumbo frets. Would it eat my fret crowning? No, Every slot's radius is designed to matches the frets' crowning radius. Fret crowning and both side of it will be synchronous reduced nearly a concentric arc if use correct action. Would it leave a shiny surface? Each slot is 200 grits, just like use 200 grits sandpaper do this work, an smooth surface will given. If has strict requirement for the smoothness of the surface, we also provide Baroque Fret Erases to obtain a buttery-smooth surface. Click seller name "Vencetmat Musical" to get it. What's the difference between it and other normal file? Diamond is the most hardness material available in the earth. Diamond coating slot greatly improved work efficiency about frets work. And, it works on any material, likes stainless steel frets. These works are difficult for other normal files. How long will it last? Long-Time Service. Diamond hardly wear out,You can use it almost all the time. Would it scratched the finger board? Yes, We suggest use at lease 3Ply tape to protect fingerboard before working. Is it good control, sturdy? Yes, solid wood handle, carbon steel body, heavy duty, quanlity can be touch. What does it give me? One file, All frets leveling. Package Contents: Fret File x 1. Oxford Bag x 1. User Instructions x 1.