With countless types, sizes, and variations of bearings available, manufacturers use a standardised designation system to identify the key characteristics of each bearing. For anyone involved in specifying, sourcing, or maintaining bearings, understanding this system is essential.

In this blog post, we’ll break down how the bearing designation system works and what the numbers and most common letters on bearings mean. You will find out how to interpret them and why this knowledge can save time, reduce errors, and improve equipment compatibility.

Whether you’re a seasoned engineer, a buyer, or just getting started in the world of bearings, this guide will help you navigate the codes with confidence.

Boundary dimensions and bearing designation codes

Bearing boundary dimensions are required for bearing installation with the shaft or housing, as described in the pictures below. They include the bore diameter, outside diameter, width, height, and other dimensions. 

Radial bearings 
(tapered roller bearings not included) 

d: nominal bore diameter 

D: nominal outside diameter 

B: nominal assembled bearing width 

Tapered roller bearings 

d: nominal bore diameter 

D: nominal outside diameter 

T: nominal assembled bearing width 

B: nominal inner ring width 

C: nominal outer ring width

Thrust bearing 
(single/double direction) 

d: shaft race nominal bore diameter 

d1: shaft race nominal outside diameter 

d2: central race nominal bore diameter 

d3: central race nominal outside diameter 

D: housing race nominal outside diameter 

D1: housing race nominal bore diameter 

T: single direction nominal bearing height 

T1: double direction nominal bearing height 

B: central race nominal height 

Boundary dimensions for metric bearings

The boundary dimensions for metric bearings are standardised in the ISO general plans

• ISO 15 for radial rolling bearings, except insert bearings, some types of needle roller bearings and tapered roller bearings
• ISO 104 for thrust bearings
• ISO 355 for tapered roller bearings

The ISO general plan for radial bearings provides several series of standardised outside diameters for every standard bore diameter. They are called diameter series and are numbered 7, 8, 9, 0, 1, 2, 3 and 4 (in order of increasing outside diameter). Within each diameter series, different width series exist (width series 8, 0, 1, 2, 3, 4, 5 and 6 in order of increasing width). 

The standard classification system

The standard classification system includes:

• Prefixes
• Base designation
• Suffixes

Bearings according to ISO general plans have the same boundary dimensions when they share the same bore diameter and dimension series. 

Bearings according to ISO general plans have the same boundary dimensions when they share the same bore diameter and dimension series. 

Bearing base designation

A bearing designation typically contains three to five digits. The basic designation explained above is a combination of number and letters with the following meaning: 

• The first digit/letter/combination of letters identifies the bearing type and a basic variant.
• The following two digits identify the ISO dimension series. The first digit indicates the width or height series (dimensions B, T or H). The second digit identifies the diameter series (dimension D).
• The last two digits of the basic designation identify the size code of the bearing bore.

Prefixes and suffixes

Prefixes provide and identify separate parts of bearings and the material they are made from. Suffixes give some additional details related to bearing design, variant, tolerance class, clearance class, lubricant used, etc. Suffixes must always be considered in relation to the bearing type. Also note that not all suffixes are standardised. 

Examples of the most common prefixes used (also used with Codex bearings)

SS – bearing made from Stainless Steel 

Examples of the most common suffixes used (also used with Codex bearings)

RS – Bearing with seal on one side 

2RS – Bearing with seals on both sides 

Z – Bearing with shield on one side – metal 

ZZ – Bearing with shields on both sides – metal 

Cx – radial clearance (x = clearance class) 

M – solid brass cage design 

TN – polyamide cage design 

MB – inner ring guided solid brass cage 

Px – tolerance class per ISO 492 

Sx – Thermally stabilised for operating temperatures 

Do you need assistance with bearing designation?

Codex Team is ready to help you with expertise & further information.