3M T-6 Lock Ring Wrench

Lock ring wrench, made for the 3M Xtract™ Electric Random Orbital Sander. Might fit their other sanders but I've only got the one. 

Fitted to a screwdriver with ~8mm diameter shaft. Normally this is a fairly expensive tool, usually around $60-$70 individually, more if you buy the repair/maintenance kit from 3M. Here's an Amazon listing for one.

STL and F3D file included in upload so you can modify it however you want.

I printed this in PLA with 7 perimeters and 20% infill. It didn't take a ton of force to unscrew the lock ring so you could probably get away with less perimeters and probably infill as well.