Fully customizable D20
I have used and modified a code for a spindown D20 for MTG. All faces are customizable, so you can change the numbers or whatever.
If you want, you can modify and use it as a regular D20, but is intented to be a spindown counter.
If you want to have a symbol in the die, just be sure your stl import is centered in origin.
Thanks a lot to the original author of the code ;)