From the designer:

This is a custom insert that I have designed to fit your Milwaukee Packout Drawers to store your M12 Rivet Gun. It specifically fits the Milwaukee 2 & 3 Drawer units (48-22-8443 & 48-22-8442).

This is the specific tool the insert is designed for: https://www.milwaukeetool.com.au/power-tools/impacts-and-fastening/rivet-tools/M12BPRT-0.html

American Model Number 2550

This is the ultimate modular storage solution for your Packout Drawers! Files are provided for having your insert on either the left or right side. I will have many more designs to share for the drawers soon so you can mix and match your inserts to set up your own perfect drawer units!

BELT HOOK NOTE:
If your belt hook is on the same side as what is pictured above (the left side) you will need to print the "left sided" files. If your belt hook is on the opposite side of the tool, you will need to print the "right sided" files which are the same designs except mirrored. By doing so, this ensures that your tool sits flat without the belt hook underneath which would prevent the tool sitting flat.