BowJax Speed String Sleeve Black 4pk. Strategically places weight on your bowstring to gain velocity. Can be used with or without string silencers. Eliminates the need for speed buttons. Silences while improving speed. Installs by slipping over the string(bow press required). Weigh 16 grains each. 4 per pack. Colors: Black Features: Helps to eliminate string oscillation while improving speed Can be used with or without string silencers Weigh 16 grains each