NSK 638ZZ 8x28x9 Deep Groove Ball Bearing

NSK 638ZZ 8x28x9 Deep Groove Ball Bearing

NSK 638ZZ is a single-row deep groove ball bearing with nominal dimensions 8x28x9 mm. NSK documentation confirms an 8 mm bore, 28 mm outside diameter and 9 mm width for 638ZZ. The ZZ suffix identifies the version with metal shields on both sides.

NSK 638ZZ - Technical Characteristics

NSK 638ZZ Dimensions

The nominal boundary dimensions are:

d = 8 mm - bore diameter

D = 28 mm - outside diameter

B = 9 mm - bearing width

Complete dimensional designation:

8x28x9 mm

These three dimensions are fundamental when identifying a replacement bearing.

638ZZ Bearing Construction

NSK 638ZZ is a single-row radial deep groove ball bearing.

Its basic construction consists of:

inner ring

outer ring

balls

cage

metal shield on both sides

The deep raceway geometry is designed primarily for radial loads and also enables the bearing to accommodate axial loads in both directions within the operating limits of this bearing type.

What Does ZZ Mean on NSK 638ZZ?

The suffix:

ZZ

identifies a bearing fitted with metal shields on both sides.

The shields help protect the internal rolling elements and raceways from larger external contaminants while helping retain lubricant inside the bearing.

A ZZ shielded bearing should not be confused with a bearing fitted with contacting elastomer seals.

This distinction can be important for speed, friction, contamination protection and application requirements.

638ZZ vs 638

The basic bearing designation is:

638

The complete shielded version is:

638ZZ

The ZZ suffix is technically significant because it identifies the double-shielded configuration.

When replacing an existing bearing, the complete designation marked on the original component should therefore be checked rather than relying only on the basic number 638.

Radial and Axial Loads

As a deep groove ball bearing, NSK 638ZZ is designed primarily to accommodate radial loading.

The deep groove raceway geometry also enables this bearing type to accommodate axial loading in both directions.

The allowable load in a specific installation depends on operating speed, lubrication, fit, temperature, load direction and other application conditions.

Product-specific dynamic and static load ratings should be taken from the applicable NSK technical data for the exact bearing version rather than from another manufacturer's 638ZZ bearing.

Double Metal Shields

The two metal shields distinguish 638ZZ from open or elastomer-sealed versions.

Their main functions are to:

• help retain lubricant within the bearing,
• limit entry of larger contaminants,
• protect the internal rolling contact area without using a conventional contacting rubber seal.

The shield configuration should therefore be considered when selecting a replacement.

Selecting an NSK 638ZZ Replacement

For replacement identification, verify:

manufacturer: NSK

designation: 638ZZ

d = 8 mm

D = 28 mm

B = 9 mm

single-row deep groove ball bearing construction

metal shields on both sides

Any additional marking on the removed bearing should also be checked.

Identical 8x28x9 mm dimensions alone do not prove complete technical interchangeability if another bearing has different seals, shields, internal clearance, precision or another special execution.

Technical Specification

FAQ

What are the dimensions of NSK 638ZZ?

NSK 638ZZ measures 8x28x9 mm: 8 mm bore diameter, 28 mm outside diameter and 9 mm width.

What type of bearing is NSK 638ZZ?

It is a single-row deep groove ball bearing, also described in technical documentation as a single-row radial ball bearing.

What does ZZ mean in NSK 638ZZ?

ZZ means that the bearing has metal shields on both sides.

What is the bore diameter of NSK 638ZZ?

The bore diameter d is 8 mm.

What is the outside diameter of 638ZZ?

The outside diameter D is 28 mm.

What is the width of NSK 638ZZ?

The bearing width B is 9 mm.

Is NSK 638ZZ a sealed bearing?

It is more precisely described as a double-shielded bearing. ZZ indicates metal shields rather than contacting elastomer seals.

Is every 638ZZ 8x28x9 bearing interchangeable with NSK 638ZZ?

Not automatically. Dimensions and double shielding are fundamental comparison points, but internal clearance, precision, cage execution and other application requirements should also be checked where relevant.

AI Overview

NSK 638ZZ is a single-row deep groove ball bearing 8x28x9 mm with metal shields on both sides. Its boundary dimensions are d = 8 mm, D = 28 mm and B = 9 mm. The ZZ suffix identifies the double-shielded configuration, an important feature when selecting or replacing the bearing.