Grover 409 Series tuning machines for "A" Style 8-string mandolin with 23mm post spacing. Nickel finish with black buttons. Professional “A” Style model mandolin machine heads are the latest in technology. A specially designed, adjustable 18:1 ratio worm gear along with the die-cast base, maintains the center lines of the gear and worm to ensure correct alignment for the finest tuning possible. Featuring a “rounded washer head” button screw for a more vintage look. Mounting screws and bushings included. Features Grover's lifetime guarantee.