Quick answer
Measure the bore diameter (d), outside diameter (D) and width (B) in millimetres. For tapered roller bearings, distinguish overall assembly width (T) from individual ring widths. Dimensions narrow the options; they do not establish interchangeability.
Read the designation
Record every letter, number and suffix visible on the bearing and packaging. A base model alone may omit important design details.
Measure the boundary dimensions
Use a suitable measuring instrument and record bore, outside diameter and width with units. Photograph the complete bearing and its markings.
Confirm operating conditions
Check load direction, speed, fits, lubrication and service conditions. Matching dimensions do not prove equal capacity or precision.
Further technical reading
Selection depends on the full designation, operating conditions and confirmed manufacturer data. Use this guide to prepare your requirements.