Sperzel "D-thing" drop tuner. Instantly and accurately detunes your E string to D with the flip of a lever. Includes screw-in bushing. Requires 10mm peghead holes. Single-pin mount.
A universal replacement unit drop tuner that is easy to install and simple to use, the D Thing is an absolute marvel of engineering and design. The flip mechanism works by locking the tuning peg into a short range of motion.
To set it up, unlock the locking lever and tune the string to pitch by holding the flipper against the plate on the E side. Once the string is tuned, continue holding the flipper on the E side of the plate and lock the arm. Next, push the flipper over to the D side of the plate and fine tune the pitch using the fine tuning knobs.