Compressor wheel extruder indicator

This model is a slightly modified version of blecheimer's Compressor Wheel. It's been scaled down to about ~34mm OD, and I added a thicker base with a 5mm-ish-deep hole in the center shaped to fit on the end of a NEMA17 output shaft. The fit is pretty tight by design, so you might need to open it up a tiny bit with fine-grit sandpaper (a deburring tool works too).

This indicator was designed to fit on a Creality Ender-3 stock extruder without impeding access to the idler-lever. Obviously, feeding new filament through the extruder blind is a little more difficult, but if you get the fit right, it's not hard to pop the indicator on and off as needed.

Also, I recommend you don't print the indicator in the same color as the rest of your printer. As you can see from the photo, I had to add some contrast to make it more visible.