I'd imagine they are fairly simple. There would be three parts; the inner ring(this is the one with the prongs you insert into the keyway), the outer ring(the one you spin) and the spring.
Here is how I think they are assembled. Imagine the first square as the inner piece. Imagine the notch in the square as a notch in the circle. Then think of the = signs as a spring running around a 1/4 of the perimeter of the circle.
- Code: Select all
------------
| | == |
| =|
| |
------------
This is what the outer piece would look like. Imagine the notch as a notch that the spring fits into.
- Code: Select all
---------------
| |
| --|
| |
---------------
The problem is that these things are probably hard to take apart or not meant to be taken apart at all. Your tension tool may be a little different, or may have two springs and four notches.
Of course, I may be totally wrong, I've never even used one of these tension tools.

"Lockpicking is what robbing is all about!" says Jim King.