Hosco Japan Ultimate Fret Crown Optimizer UFO1

Ultimate fret crown optimizer, four radii (1.1-1.4mm) for small-medium frets, #600 grit diamond
For those aiming at a more accurate crown shape during fret work, Ultimate Fret crown Optimizer (UFO) would be the preferred choice. It can help you restore the crown as close as the original shape in minimal strokes.
Conventional ”stick” type crown files seemingly contact frets lengthwise, but due to the fact most fingerboards are radiused it could touch the fret at a single point without even knowing where you are sanding at. This UFO, a palm size disk with the point of effort and load aligned, can transmits power straight right at the spot. You know where you want to sand visually.
You may have been dressing frets with a straight file, somehow trusting your instinct and experience. But if you take a close look at your work you might notice corners have been left unrounded or the arc has been ruined somewhat. UFO can tell you where you are filing the crown in 3 aspects at the same time: height, width, & the curve.
Filing an object with convex surface with a concave tool does make sense. For a simple crowning job a straight crown files will remain a handy tool. But for those seeking preciseness and advancement, UFO can be of your great help. To widen the field of work, having both UFO 1 & UFO 2 would be highly recommended so that you could handle a broad range of fret widths.

Ultimate Fret Crown Optimizer UFO1
Radius: 1.1, 1.2, 1.3 and 1.4mm
Size: 50mm diameter x 7mm thick
Weight: 95g
Material: Steel with nickel plating
Disk design: Palm size, easy to hold, control and see the filing point
Concave file with 600 grit diamond: For fast and easy crowning