Double Sealed - Precision Ball Bearing. INCLUDES 8 BEARINGS. This is the most popular size and Abec 7 rated bearing to fit skateboard wheels inline wheels caster wheels scooter wheels & also some hvac and industrial demands. The bearing size is 608 and has 2 removable rubber seals. The seals contain a carbon steel plate to assist in keeping the seal from being pushed and provides an effecting barrier against contamination. The bearing retainer (ball cage) is made of molded nylon. This retainer provides smooth and efficient bearing roll. These bearings are manufactured to precision abec 7 standards.