Bearing Parts Descriptions and Terminology

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Ball Bearings Components

The figures below illustrate an assembled Ball Bearing and the terms used
to describe each component:

Bearing Parts 1
  Shield type Component Parts
Shield type
Flange type Component Parts
Flange type
  External Retaining Ring type
External Retaining Ring type

About Ball Bearing Parts

When discussing ball bearing components, it's important to understand that the main parts of the ball bearing are the races and the balls. There is an outer race, which goes into a bore, and the inner race, in which the shaft rides. The balls are placed in between these two parts to create the rolling properties of the ball bearing. Without these basic parts, there is no ball bearing. That being said, there are other bearing parts to consider, like shields, cages, and flanges. Here you can find a description of some of these types of parts that are available through NMB.


The following retainers are available in most of our Ball Bearings.

Ribbon Retainer

Ribbon Retainer/Cage (Symbol R)

It is composed of two press molded steel parts. The balls are held between the two steel parts, and the tabs of one of the steel parts are bent over the second steel part to unite them together. This is the most common type.
Crown Retainer

Crown Retainer/Cage (Symbol H)

It is composed of a press molded steel part. The small difference in inner and outer diameters of the retainer allows them to be used for thin type and very small ball bearings.
Plastic Retainer

Plastic Retainer/Cage (Symbol MN etc.)

It is composed of a molded and cut plastic part. The plastics include Polyamide, Polyacetal, and so on. It is used for high speed rotation and low noise level.

Shields and Steels (Enclosures)

Steel Shield Snap Ring

Steel Shield-Snap Ring Type

NMB part number symbol : ZZ

The metal shield is a steel plate secured in the outer ring with a steel snap ring.

Steel Shield-Caulking Type

NMB part number symbol : KK or HH
JIS part number symbol : ZZ

The shield is a formed steel plate, pressed into a recess in the outer ring.

          Steel Shield Caulking

Rubber Non-Contact & Contact Seal

Rubber Non-Contact Steel

Symbol SS

Refers to NMB & JIS numbering system.
The rubber non-contact seal is constructed with a snap-fit into the outer ring.

Rubber Contact Seal

Symbol DD

Refers to NMB & JIS numbering system.
The rubber contact seal provides a positive contact onto the inner ring and is a snap fit into the outer ring.