Trampoline spring
material: spring steel/stainless steel
Wire dia:3mm-3.5mm(as usual)
Outer dia:21-35mm
free length with hooKs:5.5” 6.5” 7” 8” 8.5” 9” 10” 11”…
surface treatment: zinc plated (silver, black, gold…), nickel plated, electrophoresis…