These Kluson steel replacement adapter bushings are intended for converting a modern 10mm drilled headstock to accept a vintage Kluson stamped steel tuning machine with the original US 1 or 4 inch (6.35mm) string post diameter. Many repair shops and guitar luthiers use these to convert a vintage instrument back to original peg head specs.If you want to install Kluson push-fit bushes to a current U.S.A. Fender neck that are drilled out to 10.5mm instead of 10mm, please use part code MBCF65N. If you need adapter bushings to fit a 10mm headstock hole to use with 6mm "metric" tuning machines, such as Gotoh's Magnum Lock posts, please see MB65LN. Important Dimensions:Outside diameter = 9.98mmInside diameter = 1 or 4 inch or 6.35mm Note: Due to the light and screen setting difference, the item's color may be slightly different from the pictures. Please allow slight dimension difference due to different manual measurement.