Alex drawer can use a 7x12 grid for the gridfinity system, but while the 7 grid fits perfectly inside the width of the drawer, there is a small gap left on the length of it with 12 base.

None of the spacers that I found online filled the gap completely. This one is the perfect size, and your precious gridfinity won't move inside the drawer anymore.

You need to print 2 of them for each drawer, install them at the back of it before inserting your bases. They don't cover the full width of the drawer as it is not necessary, and it would use more material.

I printed mine with PLA - 0.28 layer height - 10% infill