This is the Pitch-Key PK-01. I used it only once. I'm selling it because I couldn't get the hang of it. It works without any problems. No claims and no returns, please. ・Instant purchase OK ・We do not accept price negotiations or dedicated listings Reference price: 3960 yen (Sound House) The following is quoted from Amazon: The Pitch-Key PK-01 is a revolutionary part that can be installed between the nut and tuning post (peg) of your favorite string to instantly change the tuning. You can set another preset tuning for a specific string and switch instantly by turning the wheel. It is easy to install and remove, and there is no need to modify the guitar itself or remove the strings. For example, you can instantly change from regular tuning to drop D or drop C by simply operating the Pitch-Key. You can also easily switch between overall tuning down or capo tuning on stage by attaching one Pitch-Key to each string. The Pitch-Key can be attached to almost all electric guitars and acoustic guitars, except for some guitars with special structures, headless guitars, and guitars that use a locking nut. You can instantly switch tunings and play different parts of a song. Instant drop D is of course possible, as well as switching to many other tunings.