From the designer:

This is a custom insert that I have designed to fit your Milwaukee Packout to store your M12 Die Grinder (90 Degree) and accompanying kit. It specifically fits the Milwaukee 48228435 PACKOUT Compact Organiser.

The specific M12 Die Grinder that this is designed for is model M12FDGA-0, link is provided here: https://www.milwaukeetool.com.au/power-tools/metal-working/die-grinders/M12FDGA-0.html

The design was also upgraded on 3/5/23 to accommodate a larger variety of batteries. Here's a full list of the batteries that are now compatible:

Standard M12 Batteries: 2.0Ah, 3.0Ah, 4.0Ah & 6.0Ah (I was unable to source the 6.0 but as best as I could determine, the 6.0 uses the same shell/housing as the 4.0, so it should also fit)

High Output M12 Batteries: 2.5Ah & 5.0Ah