Proper Rubber Stopper Orientation
While the WondrBolt Rubber Stopper will slide onto a Wondrbolt regardless of the stopper's orientation, there is a small difference between each side of the stopper which makes it function better in one way vs the other.
Looking carefully at the stopper, you will see that one side has a lip on the edges while the other side does not. That lip raises the edge of the stopper a little more than the rest of that surface. The purpose for this is to allow room for the small amount of tearing that occurs when a piece of cardboard is punctured with the hole punch. By placing the stopper's raised 'lip' against the cardboard instead of the flat side of the stopper, you can get the stopper to fit flush against the cardboard instead of being uneven against the side of the cardboard.
If you look at a Wonderbolt carefully, you will see that it also has a lip, which serves the same purpose.