Double sided diamond file for coarse sharpening and re-setting old blades. This is what we use when you send in battered old shears and secateurs with nicked and chipped blades - the #120 side eats through the steel to a new edge, then the #300 gives a crude finish before moving over to a whetstone to get a decent edge. Use dry. Indispensable.
Essential for fixing damaged blades, but also useful for sharpening rough edges like mower blades.