It is quite amazing how many different models can be built using just two classic K'NEX components - the connector 5-way yellow and the rod 86mm yellow.
These two parts can be connected imaginatively via a combination of end-on and side-on connections, to create a wide range of model types and sizes.
The tower in the photo shows a simple example of such a model.
The "Just Yellow" pack contains:
120 x K'NEX Rod 86mm Yellow 90 x K'NEX Connector 5-way Yellow