I decided I wanted to diffuse the beam on my Streamlight Microstream. The walls are about 1mm thick across the top and about 1.5mm around the sides so I could have a recessed lip to catch the edge of the flashlight to prevent it from being pushed to in to far.

I couldn't get a good picture to demonstrate the diffusion level, but I can report that it works well enough for me to feel good about posting it. It snaps on firmly and the cap has not popped off after a few days of carrying it in my pocket.

You could probably print it in red as well and that would be a bit better for nighttime use. If I end up giving that a try I'll upload a picture of that as well.

If you print with the cap against the bed you shouldn't need any supports.