Shown here is a 198-piece set focuses on investigating and experimenting with gears.
From the product description:
These K'Nex kits inspire young minds and satisfy kids' curiosity on how to construct simple machines. Each innovative kit keeps young builders busy and intrigued for hours at a time.
This Gears Kit builds seven different models and allows kids to work solo or as a team. The models demonstrate spur, crown, chain and sprocket gear assemblies. Includes a compartmentalized storage case with snap-on lid. Curriculum sold separately.
Here is the link for the K'NEX Intro to Simple Machines: Gears set.