Adjustable mount for laser module

This thing will hold a laser module pointed in a certain direction.

I use two of them mounted on adjacent sides of my 3D printer, to ensure that the build platform is level. I first take the platform to the home position (the one it assumes while it waits for the extruder to heat up). Then I move both lasers so that they meet exactly at the platform's corner, and it's only one bright dot, not two. Then I move the platform around. If it's level, I see only a single dot all the time.