With proper care and maintenance your bushings should last for years. Keep out of extreme heat or cold for maximum longevity. If you need to replace for any reason this bushing will make your Surf Adapter ride good as new. Duro is a measure of hardness, harder bushings have more resistance. Consider that lighter riders will likely prefer softer bushings and heavier riders will prefer harder bushings. 90a is the softest bushing. Best for skilled riders or youth who enjoy a very loose turn radius. 92.5a is quite soft. Suitable for people who love an extremely loose feeling, or youth riders. 95a is standard. It's a happy medium and leans toward the looser side at low speeds. Allowing for high performance maneuverability. 98a is a stiff bushing. It will give you more stability from low speed. Beta test these bushings and tell us what you think! Ships from: California