Hint A16 - K'NEX snap-caps
The snap-cap is a small black part that can be easily "snapped" onto the end of any K'NEX rod.
A common usage of the snap-cap is to prevent wheels falling off the end of the rod.
There are two versions of the snap-cap, as shown - a larger one for classic K'NEX rods, and a smaller one for Micro K'NEX rods.
The easiest way to remove a snap cap is to:
1. add a larger connector or a wheel onto the rod, next to the snap cap.
2. hold the rod in one hand, and with the other hand, push the connector or wheel in the direction of the arrows.