Hint G2 - Snap-on gears
Most K'NEX gears have a hole right through the middle, and can be positioned anywhere along a classic K'NEX rod.
However, the snap-on gear provides an alternative approach, in that it fits onto the end of a classic K'NEX rod. It can then spin freely, making it useful for instance for models where a gear train of three of more gears is to be used.
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