A very useful tool when treating surfaces, e.g. woodworking. 
With these tetrahedrons both sides of the board can be treated immediately. Only minimal traces are left at the contact points.
They are about 20mm high and as it is a tetrahedron, they are always the same height regardless of which side they are on. 
They can of course also be scaled larger. I don't recommend a smaller size, otherwise the underside could dry too badly.

If you like check out my other designs too!