This is a custom insert that has been designed to fit your Milwaukee Packout to store your M12 Power File and accompanying kit. It specifically fits the Milwaukee 48228435 PACKOUT Compact Organizer. Design by Jonah Pope.
 
The specific M12 Power File that this is designed for is model 2482-20, link is provided here: https://www.milwaukeetool.com/Products/2482-20
 
It should also fit the alternate model with the shorter arm, as that appears to utilise the exact same main body. This is model number 2483-20.
 
https://www.milwaukeetool.com/Products/Power-Tools/Metalworking/Sanders-and-Polishers/