Fein 63502118016 2-1/2-Inch Segmented Carbide Grout Removal Blade
This blade is designed to remove grout from standard grout lines 5/64-inch and bigger.  The oscillating action of the tool vibrates the grout out without damaging the tile on either side of the grout line.  The carbide coating on the blade allows for rapid grout removal from in between tiles.  The segmentation allows for removing one tile at a time as well as grout removal against a wall without damaging the wall.