This spring was $4.99 at my local hardware store. Made of stainless steel. Great quality.
Comparison to stock derbi 3 weight spring:
Installed in derbi rear pulley cam:
Results: in my friends 80 metra piston port it has great low end pretty much spot on with what you would tune a tjt or 6 weight to. I also machine my 3 weight variator cheeks down to allow it to variate further. Didnt loose any top speed from this.
linda please put this in the wiki.