Set of 20 springs Extreme Sport Edition – 21.5 cm – for trampoline 12Do your trampoline springs need to be replaced? This Extreme Sport Edition spring set is suitable for the round trampolines 12 with a diameter of 365. Extreme Sport Edition springs are suitable for experienced jumpers who want to go for spectacular jumps. The springs are extra safe, because there is a rubber cap around the ends. How do you measure the trampoline spring? Not sure if this is the right size spring for your trampoline? Then measure the spring. You do this by measuring from hook to hook as soon as the spring is not tensioned.