Somehow a drive pin on my Pro-Line Pro-2 SC Buggy sheared in half which resulted in a lost drive cup and set screw. If you have the ProTrac axle kit (6099-00) and need replacement parts you can purchase this kit if you only need the small parts minus the axle and driveshaft. Pro-Line doesn't specifically state that this kit is compatible with 6099-00, but I decided to give it a try instead of purchasing the more expensive ProTrac axle kit just for the 3 small replacement parts. I measured the original axle parts on my Pro-2 Buggy with some calipers and compared them with the parts from this kit and they were all dimensionally identical. Everything assembled perfectly. I'm reserving one star because I can't speak to the durability of that one sheared drive pin.