This is a custom insert designed to fit your Milwaukee Packout to store your M12 Stubby Impact (3/8) plus the FULL 43 Piece Milwaukee Shockwave Impact Socket Set . It specifically fits the Milwaukee 48-22-8435 PACKOUT Compact Organizer.
The specific tool this is designed for is model 2554-20, link provided here: https://www.milwaukeetool.com/Products/2554-20
And the specific Socket set it accommodates is the "43PC SHOCKWAVE Impact Duty™ 3/8" Drive SAE & Metric Deep 6 Point Socket Set." Link here: https://www.milwaukeetool.com/Products/49-66-7009