Kai -
Normally, you don't need any tools at all to attach a lens to a lens board. You unscrew the rear element of the lens, and then unscrew the retaining ring from the front element. Insert the front element into the hole in the lens board (from the front), and screw the retaining ring onto the back, making sure that the lens is aligned the way that you want. Tighten as much as you can with your fingers only. Then, carefully screw the rear element into the front element - carefully because the threads are fine, and you really don't want to have to deal with cross threading.
You really don't need a "spanner", although I agree that it would be nice to have one - it's on my list, but there is a bunch of other things that I would rather have first.