SKF W 618/4 4x9x2.5 mm - Stainless Steel Deep Groove Ball Bearing

W 618/4 SKF 4x9x2.5 mm - Stainless Steel Deep Groove Ball Bearing

W 618/4 SKF is a miniature, single-row stainless steel deep groove ball bearing manufactured by SKF. It has dimensions of 4x9x2.5 mm, including a 4 mm bore diameter, a 9 mm outside diameter and a 2.5 mm width. The bearing belongs to the 618 dimensional series and features an open design without seals or shields. The W prefix identifies the stainless steel construction, while /4 indicates the nominal bore diameter.

Technical Specifications - W 618/4 SKF

The listed load ratings and speed values refer to the SKF catalogue specification for W 618/4.

Catalogue speed ratings are reference values and do not guarantee that the bearing can operate at these speeds under all installation and operating conditions.

What Does W 618/4 SKF Mean?

W - Stainless Steel Bearing Construction

The W prefix in SKF bearing nomenclature identifies a stainless steel deep groove ball bearing.

Stainless steel provides improved corrosion resistance under certain environmental conditions compared with conventional bearing steel.

However, stainless steel does not provide complete resistance to all chemicals, moisture, chlorides or aggressive environments.

Actual corrosion resistance depends on the specific material, temperature, environmental conditions and exposure time.

618 - Bearing Dimensional Series

The designation 618 identifies a dimensional series of deep groove ball bearings with a relatively small cross-section.

Bearings in this series have compact outside dimensions relative to their bore diameter.

This makes them suitable for mechanisms with restricted installation space.

However, smaller dimensions do not imply the same load-carrying capacity as larger bearings with an identical bore diameter.

/4 - Bore Diameter of 4 mm

The designation /4 identifies a nominal bore diameter of 4 mm.

The slash is an integral part of the original SKF designation and must be preserved.

The complete bearing designation is W 618/4.

Open Design Without Additional Sealing Suffixes

The designation W 618/4 does not include suffixes indicating contact seals or metal shields.

It identifies an open bearing design.

It must not automatically be considered equivalent to variants with additional sealing, shielding or special construction suffixes.

Construction of W 618/4 SKF

Miniature Single-Row Deep Groove Ball Bearing

W 618/4 SKF uses a single row of balls positioned between the inner and outer ring raceways.

The deep raceway geometry allows the bearing to support radial loads and appropriate axial loads in both directions.

Its compact construction is intended for rotating mechanisms where limited installation space and low friction are important.

Inner Ring - 4 mm Bore

The inner ring has a nominal bore diameter of 4 mm.

It is designed for installation on a shaft with an appropriate diameter and tolerance.

In miniature bearings, even small dimensional deviations can affect operating clearance, rotational resistance and bearing service life.

Outer Ring - 9 mm Outside Diameter

The outer ring has a nominal outside diameter of 9 mm.

This allows the bearing to be installed in a compact housing bore.

The housing must provide adequate support without causing excessive deformation of the bearing rings.

Bearing Width - 2.5 mm

The bearing has a nominal width of 2.5 mm.

This dimension is particularly important when designing compact rotating assemblies.

It must be considered when selecting spacers, locating components and axial supporting surfaces.

Open Bearing Design

W 618/4 SKF does not have factory-installed seals or shields covering the rolling elements.

The open construction allows lubricant to reach the bearing interior but requires appropriate contamination protection within the mechanical assembly.

The lubrication method must be selected according to the equipment design and operating conditions.

Load Ratings and Rotational Speeds

Basic Dynamic Load Rating C - 0.364 kN

The catalogue basic dynamic load rating is 0.364 kN, equivalent to 364 N.

This parameter is used when calculating the nominal fatigue life of a rolling bearing.

It does not represent the maximum permissible force under all operating conditions.

Basic Static Load Rating C0 - 0.114 kN

The catalogue basic static load rating is 0.114 kN, equivalent to 114 N.

This parameter is used to evaluate loads that may cause permanent deformation at the contact points between the balls and raceways.

Fatigue Load Limit Pu - 0.005 kN

The catalogue fatigue load limit is 0.005 kN, equivalent to 5 N.

The Pu parameter is used in bearing life calculations that account for loading, lubrication and contamination conditions.

It must not be interpreted as the maximum permissible operating load.

Reference Speed and Limiting Speed

The SKF catalogue specifies the following values for W 618/4:

• Reference speed: 140,000 r/min.

• Limiting speed: 85,000 r/min.

These are two different technical parameters.

The reference speed relates to thermal conditions defined by SKF's calculation methodology.

The limiting speed reflects restrictions associated with bearing construction.

In actual operation, permissible rotational speed also depends on lubrication, loads, mounting fits, temperature and the design of the complete assembly.

The reference speed must not be interpreted as an unconditional permissible operating speed.

W 618/4 SKF vs Other Miniature Bearings

W 618/4 vs 618/4

Both designations refer to the same nominal dimensions of 4x9x2.5 mm.

The W prefix identifies SKF stainless steel construction.

A bearing without the W prefix must not automatically be considered identical in terms of material.

When selecting a replacement, the material, load ratings and operating requirements must be verified.

W 618/4 vs W 617/4

These bearings differ in outside diameter and width.

They are not directly interchangeable in terms of dimensions.

W 618/4 vs W 619/4

W 619/4 has a larger outside diameter and greater width.

It must not be used as a direct replacement for W 618/4 without modifying the housing and available installation space.

Alternative Designations and Reference Numbers

Natural written variations of the same product designation include:

• W 618/4 SKF

• SKF W 618/4

• W618/4 SKF

• SKF W618/4

• W 618/4 4x9x2.5 mm

• SKF W 618/4 4x9x2.5 mm

The complete designation W 618/4 should be preserved in technical documentation and purchasing orders.

The W prefix must not be omitted because it identifies the stainless steel construction.

Selection and Interchangeability of W 618/4 SKF

Before purchasing, verify the following:

• Complete bearing designation W 618/4.

• Required shaft diameter of 4 mm.

• Housing bore diameter of 9 mm.

• Available installation width of 2.5 mm.

• Required bearing material.

• Radial and axial loading conditions.

• Required bearing service life.

• Rotational speed.

• Lubricant type and lubrication method.

• Exposure to moisture and contamination.

• Required radial internal clearance.

• Mounting fits and tolerances.

Is Every 4x9x2.5 mm Bearing Interchangeable?

No.

Matching dimensions are necessary for dimensional interchangeability but may not be sufficient for technical equivalence.

The bearing material, construction, load ratings, precision, internal clearance and lubrication arrangement must also be considered.

For applications requiring corrosion resistance, particular attention should be paid to the stainless steel construction.

Applications of W 618/4 SKF

Due to its miniature dimensions and stainless steel construction, W 618/4 SKF may be considered for small rotating mechanisms requiring:

• A nominal shaft diameter of 4 mm.

• Very limited installation space.

• Single-row ball bearing construction.

• Stainless steel components.

• Appropriately designed lubrication and contamination protection.

Potential applications for bearings of this type include miniature precision mechanisms, measuring instruments and compact mechanical assemblies.

These are general application areas based on the bearing construction, not confirmed OEM applications for the specific W 618/4 designation.

The final selection should be based on engineering calculations and the equipment's technical requirements.

Installation and Operating Recommendations

Clean Installation Conditions

The bearing should be installed in a clean environment.

Because W 618/4 has an open design, preventing fine contaminants from entering the ball and raceway area is particularly important.

Correct Mounting Fits

Shaft and housing tolerances must be selected according to the applied loads and the operating conditions of the bearing rings.

Excessive interference may reduce the operating internal clearance.

Correct Application of Mounting Force

When mounting the bearing onto a shaft, apply the installation force to the inner ring.

When installing the bearing into a housing, apply the installation force to the outer ring.

Mounting forces must not be transmitted through the balls.

Lubrication

The open construction requires a suitable lubrication arrangement within the mechanical assembly.

The exact type or quantity of any factory-applied lubricant must not be assumed without confirmation.

Storage

Store the bearing in a clean, dry environment, protected against moisture, contamination and mechanical damage.

Frequently Asked Questions - W 618/4 SKF

What Are the Dimensions of W 618/4 SKF?

The bearing has a 4 mm bore diameter, a 9 mm outside diameter and a 2.5 mm width. Its principal dimensions are 4x9x2.5 mm.

Is W 618/4 SKF Made of Stainless Steel?

Yes. The W prefix in the SKF designation identifies stainless steel construction.

Does W 618/4 SKF Have Seals?

No. W 618/4 is an open bearing without factory-installed seals or shields.

What Are the Load Ratings of W 618/4 SKF?

The catalogue basic dynamic load rating C is 0.364 kN, and the basic static load rating C0 is 0.114 kN. These values are used in load assessment and bearing life calculations.

What Does /4 Mean in W 618/4?

The designation /4 indicates a nominal bore diameter of 4 mm. The slash is an integral part of the original bearing designation.

Are W 618/4 and 618/4 Identical Bearings?

They must not automatically be considered identical. In SKF nomenclature, the W prefix indicates stainless steel construction. A version without W may use a different material.

Can W 618/4 Be Used in Humid Environments?

Stainless steel provides improved corrosion resistance under certain conditions, but the bearing has an open construction. Moisture and contamination exposure must be considered, and suitable protection and lubrication must be provided.

Can W 618/4 Be Replaced with a Larger Bearing Having a 4 mm Bore?

Not without verifying the outside dimensions and installation requirements. An identical 4 mm bore diameter does not guarantee interchangeability.

W 618/4 SKF - Key Technical Information

W 618/4 SKF is a miniature, single-row stainless steel deep groove ball bearing with dimensions of 4x9x2.5 mm. It belongs to the 618 series and has an open construction without seals or shields. The W prefix identifies stainless steel construction, while /4 indicates a 4 mm bore. The bearing is intended for compact rotating mechanisms.

W 618/4 SKF at simmering.pl

W 618/4 SKF is offered by simmering.pl, a specialist supplier of rolling bearings and industrial mechanical components.

We serve individual customers, mechanical workshops, equipment manufacturers and industrial maintenance departments.

Our warehouse and order processing operations are located in Lublin, Poland.

We supply customers throughout Europe and offer worldwide shipping.

We also assist customers in identifying miniature SKF bearings by their complete designations, dimensions and technical requirements.