For standard guitars, set of 6. The original Rotomaticﾮ with an improved higher ratio gearing. The 18:1 ratio provides for finer tuning and greater stability. The finer gears provide smoother tuning and a higher degree of backlash elimination. This new version of the Rotomaticﾮ uses the exact housing as the original. Only the gearing has changed. Includes washers, bushings, and wood screws.