I believe there should be some more types of Cogwheels, namely Mangrove, which is a vanilla wood, and Brass, which should be the most likely metal Cogwheel to be added. There can also be Zinc Cogwheels, which may look like Iron, but has a greenish undertone, just like with the Zinc Ingots and Blocks, and Gold Cogwheels, which compared to Brass, is just overall yellowish, whereas Brass has brown undertones.