Thank you for the info. My Cirkut back needs a bit of work besides gears and fans. The spring seems to have tension, but I don't know how the release mechanism works, or how to wind it (haven't tried much yet). A diagram would be helpful. I take it from your post that you are interested in selling gears, etc. As I said above, it is usually cheaper to buy rather than make, especially for a one off, although I find that whenever I buy a camera I end up with another one. At any rate I may be in the market for some gears.