The Oceanus Shock Cord is an alternate attachment to the standard rope extension which runs between the webbing attachment on the board and the stainless steel clip of the reel. Compared to the rope extension, the Shock Cord is shorter and has bungee. Having the elastic bungee can help absorb the "shock" and load of the reel going all the way out quickly. Big waves or strong currents can also pull you in one direction and your board in another, so having the Shock Cord to ease the tension is necessary to keep the reel performing well reel after reel. It's recommended to use the both the Shock Cord and Rope Extension together to get the benefit of the bungee and also the rop to keep tension off the reel while riding. Comes with Shock Cord, webbing attachment, and washer.