Evotech Performance has developed an innovated spindle/bobbin system which allows the bobbin head to rotate on impact. This is down to the aluminum spacer system that provides a solid core for the location of the nylon bobbin head. Using this system we have increased the overall durability and impact resistance of our bobbin kits. The spindle sliders/bobbins are retained by roll threaded stainless steel spindles for increased strength. The spindle slider/bobbin kits comprise of two nylon bobbins, two anodized aluminum spacers, stainless steel spindle, nuts, washers. Made from high performance engineering materials in order to protect related items in the event of a spill. Please Note: If your axle has a cotter pin fitted this would have to be removed or you can cut the original cotter pin down so it is still in the nut and then would fit inside the slider housing and the slider housing prevents it from coming out. Easy to follow online instructions to aid hassle free installation.