Etan Premium Quality Trampoline spring 220 mm. These Etan Premium springs are often used on the larger trampolines. They are flexible springs made of Dutch spring steel where zinc is incorporated in the springs. This makes it the most powerful springs available. Please note that your current trampoline also contains 22 cm springs, if you mount too large springs in your trampoline, the jumping cloth will be under too little tension and you will not jump finely anymore. To properly measure the current length of the springs in your trampoline, remove a good, unstretched spring from the frame and measure it from the end of the hook to the end of the hook.