Specifications ◆Model Name: C・A・R・D - 3/3 ◆Material: Carbon ◆Weight: 3g This is the "C・A・R・D - 3/3" spacer for the SD90, which comes standard on high-grade models like the SD510 and SDS510. What is CARD? C - Carbon fiber / Lightweight and strong carbon fiber A - Align center / Guide function to guide the tuner to the proper position R - Resonant / Eliminates the space between the tuner and the headstock, improving vibration transmission D - Defend / Prevents mounting marks and paint cracks on the headstock caused by the tuner itself This is the meaning behind the name, but the important part is "R"! ★To put it simply, its effect is: It increases the contact between the tuner and the guitar headstock, allowing string vibrations to be transmitted firmly to the neck, thus improving the sound. It's great to have an item that you can just install without any downsides and be sure it will work! When Kluson-type tuners are installed on a guitar headstock, a large cavity is created at the base of the post. When you think about it, the contact area of Kluson tuners with the headstock is very small compared to Grover-type tuners, and it's impossible to transmit string vibrations effectively to the headstock this way. This is a structural flaw of Kluson tuners, and there is no good way to improve it. Even users of vintage tuners probably considered it "play" and gave up on it. This C.A.R.D. is a revolutionary product created as a solution to this long-standing problem. With this lightness and sturdiness! And with its moderate flexibility, it achieves high adhesion. It can truly be called a product of modern science! GOTOH has already filed for a patent, so it can only be manufactured by GOTOH! For details on length and diameter, please refer to the GOTOH official website. *Machine heads (tuners) themselves are not included in this product. The item in the first photo is the product. Accessories/Parts...Tuners