This is a Brother Scanncut mat tray extender for Scan N Cut,
This keeps the mat straight and prevents it from bending down which can make your projects come off of the mat. Keeping the mat flat helps with project quality and adhesion.
 
Comes in 3 peices and will also work with other models as you do not need to use the center bar if you wish.
 
Simply clips on for easy install and removal