Modular gears for building blocks

This are some easy-to-print gears which are compatible with all major brands of building blocks technic systems.The idea behind this modular concept is easy:Easy to print (no supports, no complicate settings)Stable (gear is 4 mm and completely flat, which makes it very stable and avoids breaking)Core changeableSmall touch point on bricks (less friction)Three different cores (= types of mounting)Unlimited amount of sizes (well, limited by printer size of course)How does it work:To use the gear simply print the size you want. Then print the core you need and push it into the gear. The core fits very well into the gear, so it's not necessary to glue them together. The core has a nose on one side, as well as the gear. Just make sure that they align. Because of this nose the core will not rotate in the gear - it just feels like a full printed gear. Cores:There are 3 types of cores: fixed, movable and round.The fixed core is the one with only the cross. It fits like a normal gear, you ju