10mm Conversion Bushings Adapter Ferrules for Vintage Tuning Keys, Metal, Nickel Nickel METAL Guitar Conversion Bushings Adapter Ferrules for Vintage Tuning Keys. Brand new, never used. Color: Nickel (Item is made of metal, not Plastic). Inside Diameter: 6.1mm. Outside Diameter: 10.15mm. Top Diameter: 14mm. Total Height: 7.6mm. These bushings are used for installing Vintage tuning keys on modern 10mm tuner holes. (Normally the vintage guitar tuner bushings are 8mm diameter). Package Includes: 10mm Nickel Bushings x 6.