Choosing a bearing catalog can be intimidating and confusing - as some seem to be written in a secret code, with a series of letters and numbers that are unknown to anyone who hasn’t chosen a bearing before. 
 
Emerson Bearing Boston, a bearing company catering to Original Equipment Manufacturers (OEM) and Maintenance, Repair and Operations (MRO) markets around the world, shares tips for cracking the code and understanding how to get the most from your bearings.
 
Rolling bearings are designated by codes that indicate the construction, dimensions, tolerances, and clearances of each bearing. Tolerance is the limit of random (unintentional) deviation of a dimension from its nominal value. Allowance is the amount of designed (intentional) deviation between two mating dimensions in a fit, which, in combination with their respective tolerances, results into a maximum and minimum clearance or interference.
 
Emerson Bearing breaks it all down:
 
The codes in a bearing catalog can include any or all of these three parts: the basic code, prefixes, and suffixes. The basic code tells you what kind of bearing it is and its bore diameter (diameter of the inner ring). Prefixes indicate basic components in the bearing, and suffixes indicate any special characteristics or designs.
 
Basic Code consists of the bearing series, which indicates the type of bearing, and the bore number, which specifies the bore diameter. The bearing series can be made up of letters and/or numbers that designate the construction, diameter series, and in many cases the width series. The bore number indicates the bore diameter. If the bearing code only contains the basic code and doesn’t include any prefixes or suffixes, it means that it is a normal bearing with normal standards of form, precision, and clearance. 
 
Prefixes refer to basic bearing components and common prefixes include H for Tapered Roller Bearings-Inch, N for Cylindrical Roller Bearings-Metric, NN for Super Precision Cylindrical Roller Bearings, and S for Stainless Steel - to name just a few.
 
Suffixes indicate bearings with special characteristics or designs, including special outer forms, cages, precision tolerances, clearances, and other characteristics like heat treatment and noise behavior. The most common suffixes for internal design are E for Higher Capacity Bearings, UA for Close Axial Preload, UO for No Clearance, and UL for Light Preload. There are also suffixes for outer surface dimensions, sealings, cage materials, precision tolerances, bearing clearances and dimensionally stabilized bearings. Note that for bearings with both special precision tolerance and special clearance, the suffixes are combined.
 
“We are dedicated to helping our customers find the bearings they require," explained Steve Katz, president. “Our team of experts can assist with proper bearing selection and equip customers with the knowledge needed - which often includes deciphering bearing codes – which  helps to ensure they avoid costly pitfalls and downtime.”