Product review (1 stars): A total rip-off. Get Gardner Spring 37092G instead for 3 bucks.
At close to $30, it is a total rip-off. Some quick tests reveal that it has a spring rate of ~ 3lbs/in. Its resting length is 5.5''. When mounted it stretches from 7.5 to 13''.
So I got instead "Gardner Spring Inc - 37092G". It has the same spring rate (ensures the door will be balanced), a larger stretch (less likely to snap), uses thicker wire (ditto), and is galvanised (will resist corrosion better than the stock part's black-iron-oxide) ; Overall it exceeds the stock part in all aspects. It was a great substitute and can be had for $3/each at a parts store like McMAster Carr or Grainger.