@squirrel79 Easiest is Taulman Bridge Nylon, Taulman 910 is a good choice for harder/stiffer stuff and gears and so is Hobbykings CX12 They used to have a cheap Nylon - extremely tough and very hard to print I called it Fishing line Nylon but too many had a tough time with it so they stopped selling it but it was pure Nylon 6 - fishing line lol. The other Taulmans are good too but we use them extremely rarely. The gears in the pic are most likely 910