It’s extremely important to have properly sized and fitting bearings for any use or application, and that starts with measuring the bearing accurately and within recognized standards. Most bearings will have part numbers, allowing for the lookup of manufacturing specifications and sizes, but these can become obscured or worn off and measuring might be necessary.
You should be able to measure the length, height, and any other dimensions of a bearing by using a standard vernier caliper or measuring precisely with a ruler. Always be sure to measure the inner diameter (ID), the outer diameter (OD), and the width.
How to read bearing numbers
It’s important to be able to identify bearings and their type and manufacturer, not only for reference of specifications and measurements but also for replacement or other reasons. The first number is usually the type of bearing, the second is usually the bearing series, the third is usually the bore size, and the final characters (often letters) will indicate the sealing of the particular bearing.
There are multiple Type Codes of Bearings including 1-8, 32/T, R, N, NN, NA, BK, HK, C, K, and QJ. Series code number usually moves from 0-4, 8, 9 from light to heavy, and thin, respectively. Bore size correlates in millimeters, and shielding and sealing can move from Z, ZZ, RS, 2RS, V, VV, DDU, VR to M. Always check with manufacturers for full listings and bearing information.