This is my own version of the Corona 3 spool nut - since I wasn't impressed by the other published version on Thingiverse, and since I was designing other replacement parts already, I made this.

took a few attempts to find a proper layer height, this was made using adaptive layers from 0.16 - 0.24 mm heights, but they're very quick to make and once you have it down, you can make a few extras while you're at it.