It specifically fits the Milwaukee 48228436 PACKOUT Low-Profile Compact Organiser.

The design consists of the main tray insert and then additional inserts that slot in place that hold the smaller length driver bits. You can use one, both or none of these extra trays, it's all up to how you want to structure your kit. Regardless, you get the files for all of it!

For holding your small driver bit in this holders, you naturally want for them to sit securely with a nice friction fit but still be easily removable. To ensure you can achieve this, a file is included that's labeled "Driver Bit - Tolerance Test." This file simply has a range of holes in different diameters that are labeled. You can print this to determine which size hole you would like to use. The hole sizes range from 7mm to 7.8mm and correspond to STL files of the full trays using the different diameter holes.

The long narrow compartment was designed to hold your driver bit extensions. Through prototyping I found my 300mm extension was ever so slightly too long to fit. To fix this, a small opening has been included either end, allowing the extension to tuck in and fit inside the case. There is some room under the moulding near the handle that allows for this.