Paint mixer

Cut appropriate length of M6 threaded rod or smooth rod with 6mm diameter. Make sure the rod is straight, otherwise everything will be wonky. You can simply screw the mixer on the threaded rod, with a smooth rod you might be required to affix it somehow (i.e glue it on).

Use with a drill to stir paint (or whatever else needs stirring). Hold on to the can and don't let the mixer wobble, run on the sides of the can or knock it over. After you're done, you can pull the mixer body just out of the liquid and make it spin to fling off the extra paint. If you do it with the correct speed it should be flung from the lower ring and into the can. If you make it spin too fast, you might end up painting more than what you've bargained for. In short: use your brains and don't do anything stupid.