This listing contains 89a Durometer Inline Wheels. These wheels are perfect for outdoor skating, and utilize the standard size 608 bearing hub. The 89a Durometer rating provides a long lasting, rock hard feel. For that reason, 89a is the most popular outdoor durometer rating. The added longevity of a harder wheel gives you more bang for your buck. If you are looking for a wheel that rides a little smoother, check out wheels with a durometer rating of 86a or lower. Wheels with a harder durometer rating will feel less smooth but last longer. Listing Includes: Qty x8 Wheels, Measuring 72mm in Diameter, and 89A in Hardness. You will also receive enough Abec 5 bearings for you wheels! You will want to make sure you have the correct spacers . If you have 8mm axles you will need 8mm x 10mm spacers, if you have 6mm axles (most common) you will need stepped spacers. We have these available for purchase in our ebay store!