225PCS Plastic Gear Set Module 0.5 - Spindle Gear, Single & Double Reduction Gears, Belt Pulley for DC Motors - Compatible with RC Cars, Trucks, Robots, Helicopters - DIY Model Toy Gear Replacement Kit (225 Pieces) - Perfect for STEM Projects, Robotics, and Engineering Experiments

It's hard to complain given the price, but you should be aware that "some styles and quantities may vary slightly," as stated in the listing. In my case that means there’s one large pulley, two medium, one small and just one tiny.The best thing I can say about the kit is that the quality of the plastic pieces seems quite good, but note that there’s a difference in materials: The orange pieces seem slightly softer and more pliable where the white and other colored gears and pulleys are harder.I’m less impressed with the rubber bands. (I’d call them belts, but they don’t seem that special.) For one thing, they’re all the same size, a missed opportunity. Their elasticity is mostly comparable, though I found two that were far more elastic than the rest, and they were the same color as the firmer ones. There doesn’t seem to be any meaning to the colors in general.For the apparent initial quality, I’m thinking 5 stars, but the randomness of the assortment and the approach to the “belts” is more of a 3, yielding my 4-star rating. My intention is to use these for repair, so I'll update if there are any future successes or failures.