The Ultrajax II String Silencer has been Bowjax's most popular model with bow companies and consumers. It's been a top seller because of its effectiveness and how long they last. Ultrajax II String Silencers require a bow press, and they slip over the bow string to effectively dampen the noise, vibration, and oscillation that occurs after the shot. Bow does not lose velocity. Testing shows a usual increase of 1 - 3 fps. For compound bow users that are looking for even more dampening ability, attach a Ultrajax II to your cable.