This is an alignment tool for a Chinese k40 laser engraver.
The tool is suitable for the laser head with a diameter of 26mm. I have an aluminum tube used to align the tool in the head. You have to be careful not to damage the mirror in the head with the tube!
With the laser beam gauge you can see at which angle the beam comes from the lens. You can cut an M3 thread into the gauge to secure it with a screw on the head.
The parts I have printed from pla.
The target I have lasered from 2mm balsa.
In the last picture you can see before and after the adjust from my laser. It is not perfect but better than before.