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Bearing Anatomy

The standardized skateboard bearing is designated as the 608 series. This single-row ball bearing typically consists of an inner race, outer race, balls, ball retainer, and seal/shield closures. It is characterized by an 8mm inner bore diameter, a 22mm outer diameter (OD), and an overall width of 7mm. Most skate bearings are manufactured to an ABEC Rating, which is the industry standard for measuring the manufacturing tolerances of ball bearings. The higher the ABEC rating number, the tighter the tolerances.

See List of Bearings or Bearings for some bearing recommendations.

Bearing Nomenclature

Each number/character in a bearing part number is divided into its separate components. Each manufacturer uses their own numbers, but there are some that can be considered sort of an industry standard. Most of these don't apply to skate bearings, but here are the basic designations:

The First Number is the Type Code
Type Code Description
1 Self-Aligning Ball Bearing
2 Spherical Roller Bearing
3 Double-Row Angular Contact Ball Bearing
4 Double-Row Ball Bearing
5 Thrust Ball Bearing
6 Single-Row Deep Groove Ball Bearing
7 Single-Row Angular Contact Bearing
8 Felt Seal
32 Tapered Roller Bearing
The Second Number is the Series

The series reflects the robustness of the bearing.

Series Description
8 Extra thin section
9 Very thin section
0 Extra light
1 Extra light thrust
2 Light
3 Medium
4 Heavy
The Third Number is simply the Bore Diameter in millimeters

So, in conclusion, a 608 bearing is a single-row deep groove ball bearing, extra-light, with a bore diameter of 8mm.