The Bont 688 mini bearing has an exceptionally fine polished bearing track surface and incredibly precise balls. The light weight plastic cages allow for lower rolling resistance. The steel, which is extremely strong, helps the bearing keep its shape when under load.
Bont 688 bearing adapters fit over your 688 mini bearings so that they can fit into 608 wheels. These bearing adapters allow you to use a mini bearing 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 set up with better acceleration.
This product requires cylinder spaces, not the normal self centering spacers.