Necessary spare differential gears if you run your 1/10 RC car for many kilometers. They are as durable as the original parts, so they may not be suitable for too high performance modern cars. I used the three small cone gears as replacements in a Marui Ninja 1/10 4WD, by enlarging the center holes to 3mm and using appropriate axles. They seem to work acceptably.
I needed a small bevel gear set to make an articulated arm for my action camera, and from all options I had, this was amazing simple to use, yet effective solution for my purpose.