The original FretGuru crowning file quickly became the highest rated, best selling file on Amazon. This didn?t stop us from completely re-engineering it, resulting in a unbelievable performance improvement. At the heart of this file is the FretGuru exclusive D.I.A. (Dual Integrated Arc) cutting geometry, which gives you far more precise CUTTING CONTROL, ACCURACY and FINISH than any other file - especially diamond files - GUARANTEED! Experienced guitar geeks know there's an ideal-yet-elusive "HOLY GRAIL" for the way a fret crowning file SHOULD cut, where the file never touches the center line or "peak" of the fret top until the last few file strokes. This is especially true with freshly leveled frets, as you don't want to disturb the perfectly level "plane" you've just created by indiscriminately removing material from the fret tops with a crowning file. Ideally you want to leave the finest sliver of leveled fret along the centerline which is then polished out. Diamond files are especially guilty of this - with the random way diamond grains are applied to the cutting groove, and the stray grains that stick up higher than the surrounding grit. So how did we do it? I've wrestled for 5 years with how to accomplish this, with machinists and toolmakers just scratching their heads when I told them what the goals were and what I wanted to do. The problem with every other fret crowning file, it that they are all made using standard off-the-shelf tooling - typically ball end mills - that are only available in standard size increments, and MORE IMPORTANTLY, only available as a perfect sphere shape. But one day the "lightbulb" went off, and I ran the idea by one of the top CNC toolmakers in the country. He still didn't think it would work, but reluctantly agreed to make a prototype tool... with no guarantee, that cost more than 2 years supply of our normal tools. And the results were mind-blowing, better than I could have imagined! Try it for yourself.