Made with absolute precision and attention to detail, the SiN System Bearings are designed for nothing less than hardcore skateboarding. The shields have extremely tight tolerances helping to keep all the nasty dirt from your steel ball bearings. When they do need a cleaning, the removable C-clip shields are there to do the job.One of the fastest bearings available today. Their performance technology is so unique that they have been granted a patent by the US Patent Office No. 6,457,871.