Hint G5 - K'NEX Spacers
The primary purpose of K'NEX Spacers is to ensure that wheels and gears that would otherwise slide freely along rods are maintained in their correct position at all times.
The photo shows two 25mm black wheels held in position on a classic K'NEX rod by a Blue spacer and a Silver spacer.
There are five types of spacer, as shown in the photo opposite:
For Micro K'NEX rods:
MICRO K'NEX Spacer 6 Wide White (530600)
MICRO K'NEX Spacer 4 Wide Blue (530400)
MICRO K'NEX Spacer 3 Wide Metallic blue (512242)
For classic K'NEX rods:
K'NEX Spacer Silver (91224)
K'NEX Spacer Blue (90994)