Really effective for removing harmonics that linger at the headstock (positioned before the nut). Positioned after the nut, it significantly reduces sustain (string resonance), and/or greatly reduces vibrations of unplayed strings, and/or for the "slap" technique. A bit expensive, but well made; a really useful "pro" accessory on my 4-string bass. I recommend it! P.S.: tighten it just enough so that it is in contact with the strings and doesn't "move around." Positioned between two frets, tightened firmly, it acts as a capo on my bass (the action of my strings is set very low).