This is a gear kit, which contains 60 kinds of 0.5 modulus gear, the gear shaft 102A which there is copper gear, also the 2.3MM and 3.17MM gear included,  some rack, worm and belt may you need too.  Gear are made of ABS plastic and absolutely meets DIY requirements. By using these sorts of gear, you can diy a lot of toy models, if some missing gear parts on the model can also be found suitable to replace.