This is a replacement "tray" for the Bauer Modular Storage System Medium sized box.  It has a Gridfinity Refined baseplate with the 15mm thumbscrew to hold down the bins.  (No magnet holes).  It completely replaces the red bins.  There is a slot on the side for storage of something as the gridfinity baseplate didn't quite fill it completely.

I printed it in Overture PETG, it is a snug fit.  So make sure your printer is pretty close.  It is one piece, as I have printers large enough to print it as one, but you can whack it up in Orcaslicer and glue it back together easily, especially if you use PLA.

It is not designed to lock in, but it doesn't just slide out either, you may want to use a modifier to put a finger hole in the ends if you think you'll want to take it in and out.  For my purposes, it's permanent in the box, so I didn't.

The red bins are great, but just too big for what I needed, so gridfinity to the rescue.

It's useful for me, if somebody else can use it, great.