The latest innovation is a groove cutter which allows you to cut three different size grooves simply by switching the location of the knives. The 8" diameter cutter allows you to cut grooves in three widths, 5.5mm, 5.9mm or 1/4".To adjust the groove width simply change the location of the knives.User InstructionsThe pair of knives determines the cutting width of the cutter. There is one knife on each side of the cutter. To change the cutting width you have to change the location of both knives (Frontside and backside).