Propellers and windmills

A propeller or windmill blank comprising a planar sheet of material having markings defining a central region and two blades extending in opposite directions along imaginary lines;

• and wherein the blank has a marking or a line of preferential folding or bending inclined to the imaginary lines which, when the blank is folded or bent therealong, will result in pitch being applied to the blades;
• a portion having a marking or line of preferential folding or bending on each side of which marking or line the portion is of generally triangular shape, and means for stabilizing a fold or bend on the first said marking or line which will result in pitch being applied, a fold or bend on the second said marking or line and for securing said portion to said central region such that said portion and said central region when so secured together define a hub region of generally tetrahedral shape from edges of which said blades project.