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.

1. (optional) Use a 3mm tap to thread the small hole in the truncated sphere and the one in the circular section of the main body.
2. Place the laser module in the truncated sphere's large through hole, and secure it in place with a short M3 bolt.
3. Put the main body's beam trough the secondary body's bracket. Make sure to orient it so that the inner sides of the circular sections form a cradle.
4. Place the truncated sphere inside the cradle, and close the cradle.
5. Use an M3 bolt to join the holes in the circular section of each body. This bolt will allow you to tighten or loosen the cradle's grip on the truncated sphere
6. Use two M3 bolts to secure the main body's beam to a suitable surface