These Kluson steel replacement adapter bushings are designed to convert a modern 10mm drilled headstock to accept a vintage Kluson stamped steel tuning machine with the original US 1/4 inch (6.35mm) string post diameter. Many repair shops and guitar luthiers use these bushings to restore vintage instruments to original peghead specifications. For installing Kluson push-fit bushings on a current U.S.A. Fender neck drilled to 10.5mm instead of 10mm, use part code MBCF65N. For adapter bushings that fit a 10mm headstock hole with 6mm "metric" tuning machines, such as Gotoh Magnum Lock posts, refer to part number MB65LN. Important dimensions: outside diameter = 9.98mm, inside diameter = 1/4 inch (6.35mm).