Biltins are the first precision bearing designed for skateboarding that incorporates an integrated bearing spacer and speed rings (Most trucks come with speed rings, be sure to remove those when using Biltin Bearings). The perfectly faced inner races provides precise spacing and perfect alignment so that the locknuts can be snuggly tightened without pinching or binding the bearings. The bearings work together to more evenly share the sideloads and keep your wheels flat on the ground for better wear. This patented system is guaranteed to give you the fastest and strongest bearings on the planet. They fit all skateboard wheels that use the industry standard 10mm spacing. Super easy to clean too!