An improved file for dressing the ends of the frets, after they've been installed, trimmed flush and beveled. With one thin edge ground "safe," and the other rounded over, this file cuts only where it needs to: on both sharp corners of the unground thin edge, and on both of the wider toothed cutting surfaces.
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Dan Erlewine's Fretting Series
Complete instruction from fret basics like installation and dressing, through complex refrets and fretting for the production shop.