I found it very difficult to unscrew the cutting knives from the blender jar of my Philips HR2195/08 blender for cleaning since there is not much place to get a good grip. With this tool, you can add a solid lever to the mechanism to unscrew it easily.

I printed this with 0.2mm layer height in PETG and 20% infill. The lever is designed to print without support. The other parameters are not particularly relevant as long as the result is strong enough not to break. I tried to design this in a way that there should be no areas that will undergo particularly strong mechanical stress, such that I expect even PLA to be strong enough.