This is a remix of the bubble level by twchambers over on thingiverse. I made a few changes to make it stiffer and easier to use:

• Inverted it so that it's open towards the tripod base rather than the head
• Made the bubble level hole go all the way through, out of necessity and to lower the bubble level
• Made it taller

In this version, the bubble level sits much lower and thus doesn't interfere with the tightening screw for the pan function of my tripod head anymore. It also doesn't stick out as much, which looks better. The taller side walls make the whole thing much stiffer for better accuracy (I found that the original design was flexing quite a bit whenever I touched it).

I printed this in PLA and it works very well on my MeFoto Globetrotter CF. Thanks to twchambers for sharing his OpenSCAD design file! I'm doing the same here of course, so you can customize it. The STL and GCode files are for a 50mm base diameter and an 18mmx10mm bubble level.