Constructed of BCY DynaFlight 97 material, Excalibur Crossbow s Matrix Strings reduces creep while increasing speed. They also feature a proprietary center serving which significantly increases string life. Will fit all Matrix and Bulldog series crossbows such as Matrix 405, Matrix 380, Matrix 355, Matrix 310, Grizzly, GRZ2, Bulldog 400, Bulldog 380, Bulldog 440, Bulldog 330