This is a screw for the adjusters of violins and violas. It has been confirmed to be usable with Wittner adjusters. A purple SWAROVSKI crystal is attached to the surface. It has not been used except for taking pictures after attaching it to the adjuster. The first image is an installation example, so please understand that the screw is the only item included before purchasing. Wittner Adjuster Violin Viola A-string E-string Swarovski Adjuster