The Thruster spring is used to add resistance to turns made by the rider. The springs we use are loose enough for tight turns but strong enough not to break. SmoothStar springs do not break. SmoothStar springs are designed to compress 0.07" - 0.20" after about 20 hours of riding. SmoothStar springs are not designed to be replaced and should never be overtightened so that board is too hard to turn.