If you need to measure a bearing, it is always best to check for the part number first. The part number is engraved onto most bearings and will give you the most accurate information. However, over time these can rub off and so it may be necessary to measure the bearing yourself.
To get the most accurate measurement you will need a vernier caliper, however, if you don’t have one available a ruler can also be used.
You will need to take three measurements, the inner diameter (ID), the outside diameter (OD) and the width (W). Bearings are often referenced to by these dimensions – ID x OD x W.
Types of Bearings:
Ball Bearing – A ball bearing uses loose balls to maintain separation between the two races.
Roller Bearing – The same as a ball bearing but instead of balls, a roller is used to maintain the separation,
Needle Bearing – a small bearing which uses small rollers to reduce the friction between the races