Inline Rollerblade Axle ALUMINUM SPEED SPACER 8-Pack Spacers for 6mm Axles Lets face it. Bearings, spacers, and axles can be unnecessarily complicated so lets try and make this easy. Most inline axles have an outer diameter of 6mm. Most bearings have in inner diameter of 8mm. These spacers make standard 8mm bearings compatible with 6mm axles. This package includes 8 aluminum stepped spacers for standard size wheels and bearings These minimize drag on your bearings, the solid aluminum construction dissipates head and will last longer than other plastic This stepped spacer is for use with regular (size 608) bearings and 6mm inline axles. The bearings sit on the recessed part of the spacer, providing a seamless integration to the wheels. For use with all standard size wheels, standard size 8mm bearings, and standard size 6mm axles. To install, place 1 bearing in the wheel. Fit the spacer into the bearing already in the wheel, and insert the other bearing into the other side of the wheel. Voila!