Unlike lighter products, these slides cannot be adjusted to fill the space between the drawer and the structure to which the outer slide is attached. So you have to make sure that your box fits almost perfectly. I used these rails for a large (58" x 20" x 12") drawer that sits under a newly built bay window seat. I was delighted when the box fitted perfectly between the rails. But I believe when If they are off by 1/8 inch, they probably won't work properly.