I bought a new head for my K40 laser but the diameter of the hole in the plate that holds it was too small. Since i have no tools to machine metal i designed a plate with the same thickness that fits the head. Its not perfect but fits and works just fine :)

There are also two rings included since the smaller lens that i have was lifting up when connecting the air pressure to the head. 

The head is just not well designed for the K40, but with those small changes it works just fine!