Hint A19 - Curved rods
"Curved rods" are K'NEX rods that are manufactured with a specific length and curve radius.
There are three lengths available: 95mm Purple, 139mm Orange and 203mm Silver.
Unlike K'NEX Flexi rods, the shape of the rod cannot be changed.
The photo shows one of the many ways in which curved rods can be used to enhance a K'NEX model.