SkyBound Standard Silver 3.5 Inch Trampoline Springs - Set of 15 SkyBound Standard Silver 3.5 Inch Trampoline Springs - Set of 15 IMPORTANT: Prior to purchasing, measure your original springs from hook end to hook end, disconnected from your trampoline, and completely unstretched. For help, please contact SkyBound. SkyBound Trampoline Springs are designed to replace your trampoline's rusted, worn out, dangerous springs and return bounce to your old sagging mat. Each spring is designed to exceed your original manufacturer specifications, offering the best quality steel, the thickest steel guage, and the most coils to provide the safest, strongest, and bounciest springs. For more protection, consider SkyBound's Premium Gold Springs featuring yellow zinc plating to help ensure a longer life in humid/wet environments by helping to prevent premature rusting (oxidation).