If you use a jig or a surface grinding attachment to grind fullers, this small simple tool provides a more precise method for setting up to get the groove right where you want it. The end of the tool with the large V-shaped opening cradles a small wheel while you hold your work piece flat against the other end. The sharp tip in the middle indicates right where the centerline of the wheel is going to grind. If you scribe a line where you want the fuller to be, you can accurately align your jig before taking off any material.