Nuts, bolts, tools - this tray is so you can have a handy spot to drop them while working on your Ender 3. It's .36mm thick so it fits into the .367 slot along the side extrusion on the Ender 3 (OG). It isn't designed to slide in, it cantilevers so if you need to move your Ender 3 while working on it you can easily remove it and set it aside so items don't get lost.

This is my FIRST original make - so if you have recommendations on how to improve it, or if you remix it, be sure to share.