Bont Mini Adapters
US$24.99
These bearing adapters allow you to use a mini bearing (688 are 8mm inner diameter and 167 are 7mm diameter bearings) in a wheel that was made for a larger 608 bearing. The benefit of using a mini bearing and an adapter rather than a 608 bearing is that you can create a much lighter setup with better acceleration.
Sold in packs of 16 (for 8-wheels)