DetailsUltrajax II string silencer has been our most popular model with bow companies and consumers for the past two years. It's been a top seller because of its effectiveness. Ultrajax II slip over the bow string to effectively dampen the noise, vibration, and oscillation that occurs after the shot. They require a bow press for installation. For compound bow users that are looking for even more dampening ability, attach a Ultrajax II to your cable. These weigh 19 grains each.