I was going through an old dresser looking for various supplies and found an unexpected supply of spring to be used in designs similar to this. I found whats called a "snake" for cleaning the inside of a trombone. Here is a picture
http://images.wwbw.com/products/origina ... 144555.jpg
The spring is relatively small in diameter (about 1/4 in) but provides for a small wrench. The coils provide alot of resistance, but not so much that it would be pointless in using. They are relatively cheap (a few dollars for a couple of feet), and provide enough spring to make dozens of wrenches. Just an idea