SKF 618/4 4x9x2.5 - Miniature Deep Groove Ball Bearing

618/4 SKF 4x9x2.5 mm - Miniature Deep Groove Ball Bearing

618/4 SKF is a miniature, single-row deep groove ball bearing manufactured by SKF, with dimensions of 4x9x2.5 mm. It has a 4 mm bore diameter, a 9 mm outside diameter and a 2.5 mm width. The bearing belongs to the thin-section 618 series and features an open design without seals or shields. The standard version is manufactured from bearing steel and has normal radial internal clearance (CN).

Technical Specifications - 618/4 SKF

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

Catalogue speed ratings do not guarantee permissible operation under all conditions.

What Does 618/4 SKF Mean?

6 - Deep Groove Ball Bearing

The first digit identifies the deep groove ball bearing family.

Bearings of this type use balls running between deep raceways in the inner and outer rings.

The construction is primarily designed to support radial loads while also accommodating appropriate axial loads in both directions.

18 - Dimensional Series

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

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

This makes them suitable for mechanical assemblies with limited installation space.

/4 - Bore Diameter of 4 mm

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

The slash is an integral part of the manufacturer's designation and must be preserved.

The complete catalogue designation is 618/4.

No Sealing Suffix

The designation 618/4 does not contain a suffix indicating contact seals, non-contact seals or metal shields.

It identifies an open bearing design.

CN - Normal Radial Internal Clearance

The standard SKF 618/4 version has normal radial internal clearance, commonly designated CN.

It must not automatically be considered equivalent to a bearing with increased C3 clearance.

Operating clearance after installation also depends on mounting fits, temperature and loading conditions.

Construction of SKF 618/4

Single-Row Ball Arrangement

The bearing contains one row of balls positioned between the inner and outer rings.

The balls roll along deep raceways, allowing the shaft to rotate relative to the housing.

Inner Ring - 4 mm Bore

The bore diameter is 4 mm.

The bearing is designed for installation on a shaft with an appropriately selected diameter and tolerance.

In miniature bearing arrangements, even small deviations in mounting fits may significantly affect operating clearance.

Outer Ring - 9 mm Outside Diameter

The outside diameter is 9 mm.

The outer ring must be properly supported within the housing without excessive deformation during installation.

Bearing Width - 2.5 mm

The bearing width is 2.5 mm.

This dimension is particularly important in compact assemblies where the available space for bearing installation is limited.

Steel Cage

The cage maintains the correct spacing between the balls and reduces direct contact between adjacent rolling elements.

Its function is to guide the balls during bearing operation.

Open Construction

The bearing has no seals or metal shields.

The open construction allows lubricant to reach the balls and raceways but requires suitable cleanliness and lubrication conditions.

Additional protection may be necessary when the bearing operates in a contaminated environment.

Load Ratings and Rotational Speeds

Basic Dynamic Load Rating C - 0.423 kN

The basic dynamic load rating is 0.423 kN, equivalent to 423 N.

This parameter is used in nominal bearing fatigue life calculations.

It does not represent an unconditional maximum permissible operating force.

Basic Static Load Rating C0 - 0.116 kN

The basic static load rating is 0.116 kN, equivalent to 116 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 fatigue load limit is 0.005 kN, equivalent to 5 N.

This parameter is used in bearing life calculation methods.

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

Reference Speed - 140,000 r/min

The reference speed is a catalogue parameter associated with the thermal operating conditions of the bearing.

It does not automatically represent the permissible speed in every application.

Limiting Speed - 85,000 r/min

The limiting speed reflects restrictions associated with the bearing construction.

The permissible speed in an actual application also depends on lubrication, loading, temperature, mounting fits and installation conditions.

SKF 618/4 vs Other Bearing Versions

SKF 618/4 vs SKF W 618/4

Both bearings have identical nominal dimensions but differ in material and catalogue load ratings.

The W prefix in SKF nomenclature identifies stainless steel construction.

SKF 618/4 and SKF W 618/4 must not automatically be considered fully equivalent in technical performance.

SKF 618/4 vs SKF 617/4

These bearings have different outside diameters and widths.

They are not directly interchangeable in terms of dimensions.

SKF 618/4 vs SKF 619/4

The 619/4 bearing has larger outside dimensions.

It cannot be used as a direct replacement without checking the housing design and available installation space.

Alternative Designations and Reference Numbers

Natural written variations of the product designation include:

• 618/4 SKF

• SKF 618/4

• SKF618/4

• 618/4 4x9x2.5 mm

• SKF 618/4 4x9x2.5 mm

The designation 684 is used in some manufacturers' catalogues for bearings with dimensions of 4x9x2.5 mm.

However, dimensional compatibility does not automatically guarantee identical construction, internal clearance, material or load ratings.

Selection and Interchangeability of SKF 618/4

Before purchasing, verify the following:

1. Complete designation 618/4.

2. Manufacturer SKF.

3. Shaft diameter of 4 mm.

4. Housing bore diameter of 9 mm.

5. Installation width of 2.5 mm.

6. Required bearing material.

7. Open construction.

8. Normal radial internal clearance CN.

9. Dynamic and static load ratings.

10. Rotational speed.

11. Lubrication conditions.

12. Operating temperature.

13. Radial and axial loading conditions.

14. Environmental contamination.

15. Required bearing service life.

Is Every 4x9x2.5 mm Bearing Interchangeable?

No.

Identical dimensions provide the basis for dimensional compatibility but do not guarantee full technical interchangeability.

The material, internal clearance, cage, load ratings, precision and lubrication conditions must also be considered.

Applications of SKF 618/4

Due to its compact dimensions and deep groove construction, the bearing may be used in appropriately designed miniature rotating assemblies.

Typical application areas for miniature bearings of this type include:

• Small precision mechanisms.

• Compact mechanical equipment.

• Measuring mechanisms.

• Miniature rotating assemblies.

• Equipment with limited installation space.

These are examples based on the bearing's construction and dimensions, not confirmed OEM applications for this specific SKF part number.

Final bearing selection should account for actual loads, rotational speed and operating conditions.

Installation and Operating Recommendations

Clean Installation Conditions

The bearing should be installed in a clean environment.

Because it has an open construction, preventing dust and other contaminants from reaching the balls and raceways is particularly important.

Correct Mounting Fits

Shaft and housing tolerances should be selected according to the loading conditions.

Excessive interference may reduce radial internal clearance.

Correct Application of Mounting Force

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

When pressing the bearing into a housing, apply the mounting force to the outer ring.

Mounting forces must not be transmitted through the balls.

Lubrication

The open design requires suitable lubrication within the mechanical assembly.

The bearing must not be assumed to contain a specific type or quantity of factory-applied grease unless confirmed by the supplied product documentation.

Storage

The bearing should be stored in a clean, dry environment, protected against moisture, contamination and mechanical damage.

Frequently Asked Questions - SKF 618/4

What Are the Dimensions of SKF 618/4?

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

Is SKF 618/4 a Stainless Steel Bearing?

The standard SKF 618/4 is manufactured from bearing steel and is not identified as a stainless steel version. The stainless steel variant is designated W 618/4.

Does SKF 618/4 Have Seals?

No. It is an open bearing without factory-installed seals or shields.

What Internal Clearance Does SKF 618/4 Have?

The standard version has normal radial internal clearance, designated CN.

What Are the Load Ratings of SKF 618/4?

The basic dynamic load rating C is 0.423 kN, and the basic static load rating C0 is 0.116 kN.

Are SKF 618/4 and SKF W 618/4 Interchangeable?

They have identical dimensions of 4x9x2.5 mm but differ in material and load ratings. Interchangeability must be evaluated against the requirements of the specific application.

Is Bearing 684 Equivalent to SKF 618/4?

The designation 684 is used by some manufacturers for bearings with dimensions of 4x9x2.5 mm. The complete technical specification must be checked before substitution.

Does SKF 618/4 Require Lubrication?

Yes. As an open bearing, it requires an appropriate lubrication arrangement within the mechanical assembly, according to the application's requirements.

SKF 618/4 - Key Technical Information

SKF 618/4 is a miniature, single-row deep groove ball bearing manufactured from bearing steel, with dimensions of 4x9x2.5 mm. It belongs to the thin-section 618 series and features an open construction without seals or shields. The standard radial internal clearance is CN. It is designed for compact rotating mechanisms requiring small installation dimensions.

SKF 618/4 at simmering.pl

SKF 618/4 is available from simmering.pl, a specialist supplier of rolling bearings and industrial mechanical components.

We serve equipment manufacturers, mechanical workshops, industrial maintenance departments and B2B purchasing teams.

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 SKF bearings by their complete designations, dimensions and technical requirements.