Sometimes ideas just come from nowhere! I've opened heaps of paint cans with locking rings over the years but for some reason I opened one this last week and thought 'Toggle Clamp'. After working out the best and easiest way to make them, I built a prototype and came up with this design.
With the use of the paint can locking ring, these clamps are very easy to make. The most difficult part of the clamp (the mechanism) is already provided by the locking ring, so with a few scraps of wood a clamp can easily be completed.