These are well dimensioned copies of the NeoPixel rings that Adafruit sells:

The Jewel: https://www.adafruit.com/products/2226
12 Pixel: https://www.adafruit.com/products/1643
16 Pixel: https://www.adafruit.com/products/1463
24 Pixel: https://www.adafruit.com/products/1586
60 Pixel: https://www.adafruit.com/products/1768

I needed these for proper sizing of related features inside of Autodesk Inventor but I thought they might prove useful for other modelers.

These were printed on a Makerbot Replicator 2 using MatterHackers black PLA filament (1.75mm) with medium settings (0.2mm layer thickness, 1 shell) but aside from where the indentations for the LEDs, I think they should print well on any printer though that's not really the point for me (I use them as virtual sizing tools, not physical sizing tools though I expect they could be useful for that too).