This mechanism to open cabinet drawers is placed beneath the box. The alternative is to mount the slides to the sides of the box.
These are ball bearing slides that reduce the friction when the drawer box opens and closes for that smooth “gliding” effect. Not having these glides results in more friction, and in cold weather, occasionally the box may be difficult to shift or move. The slides are usually made of metal and few of these lock at full extension so that the box does not fall out of its space.