Deep Groove Ball Bearings

What is a deep groove ball bearing?

A deep groove ball bearing is the most widely used type of roller bearing in the world. It gets its name from the deep, uninterrupted groove machined into both the inner and outer rings. The groove radius is only slightly larger than the radius of the balls, so the balls sit closely in the raceways.

A standard bearing has four main parts:

• An inner ring, which usually fits onto a rotating shaft
• An outer ring, which usually sits in a fixed housing
• A single row of balls running between the two raceways
• A cage or retainer that keeps the balls evenly spaced.

Most single-row deep groove ball bearings are assembled using the Conrad method. 

• The inner ring is pushed off-centre so the balls can be inserted into the gap, then the balls are spread evenly, and the cage is fitted.
• This method limits how many balls can be fitted, but it keeps the raceways continuous, which is what lets the bearing take axial loads in both directions.

The bearing is non-separable, meaning the rings, balls, and cage stay together as one unit, which makes it simple to handle and fit. Rings and balls are usually made from hardened chrome steel (grade 52100). Cages are most commonly pressed steel, with polyamide and machined brass also available.

Why are deep groove ball bearings essential?

They combine versatility, simplicity, and low cost better than almost any other bearing type, which is why they are the default choice for a huge range of machines. They carry radial loads, which act along the shaft. This means a single bearing type can cover many different design needs. Their low friction makes them well suited to high speeds, and they run with low noise and vibration, which is particularly important in electric motors and household appliances. 

They need little maintenance. Sealed and Shielded versions are usually supplied pre-greased and are often designed to run without relubrication. Their boundary dimensions are standardised internationally. So a bearing of a given reference has the same bore, outer diameter, and width, regardless of which reputable manufacturer makes it. 

Typical applications include:

• Electric motors and generators
• Gearboxes and pumps
• Fans and compressors
• Washing machines, vacuum cleaners and other household appliances
• Power tools
• Automotive parts such as alternators
• Conveyor rollers
• Bicycles, skateboards and inline skates

The main types of deep groove ball bearings

• Single-row deep groove ball bearings - These are the standard design and by far the most common; they are available in a wide range of sizes, from miniature bearings with bores of a few millimeters to large bearings with bores of several hundred millimeters.
• Double-row deep groove ball bearings - These have two rows of balls in a wider bearing. They offer higher radial load capacity than a single-row bearing of the same bore and outer diameter. They are used where space in the axial direction is available but the load is too high for a single row. 
• Filling slot bearings - These bearings have a notch in the rings that lets more balls be inserted than the Conrad method allows, which increases radial load capacity. The trade-off, however, is that the slot interrupts the raceway, which reduces their ability to carry axial loads.
• Open bearings - these have no seals or shields. They have the lowest friction and are suited to oil-lubricated applications, such as gearboxes, or to housings that already provide sealing. 
• Shielded bearings (Z / ZZ / 2Z) - These have non-contact metal shields, which keep grease in and larger particles out, with very little added friction that allows them to suit high speeds. 
• Sealed bearings (RS / 2RS) - These have rubber contact seals, which are usually nitrile rubber bonded to a steel insert. They give the best protection against dust and moisture, but the seal contact adds friction and lowers the limiting speed.
• Low-friction seal bearings (often RZ / 2RZ) - These use non-contact rubber seals that sit very close to the inner ring. They offer a compromise, with better sealing than shields and lower friction than contact seals. 
• Bearings with a snap ring groove (N) or snap ring fitted (NR) - These have a groove in the outer ring. The snap ring locates the bearing axially in the housing, which can simplify housing designs. 
• Flanged bearings - these have a flange on the outer ring, which positions the bearing axially without a shoulder in the housing. They are common in miniature sizes.

Material variants include:

• Stainless steel bearings - often in grade 440C, for wet, corrosive, or hygienic environments.
• Hybrid bearings with silicon nitride ceramic balls - Lighter, harder, and electrically insulating.
• Full ceramic bearings - used for highly corrosive or non-magnetic applications
• Electrically insulated bearings - used in inverter-driven motors to prevent damage from stray electrical currents

How to choose the right deep groove ball bearing?

• Size and dimensions - The bore must suit the shaft; the outer diameter and width must fit the housing. For the same bore, a heavier dimension series has a larger outer diameter, larger balls, and higher load capacity, but takes up more space.
• Load - Work out the radial and axial loads and whether they are steady or involve shocks. Compare them with the bearing’s basic dynamic load rating and basic static load rating, which are published in manufacturers’ catalogues. Deep groove ball bearings handle moderate axial loads well, but very high or purely axial loads are better suited to angular contact or thrust bearings. 
• Internal clearance - C3 is greater than normal and is common in electric motors and wherever interference fits, or temperature differences reduce clearance in operation. C4 is larger still, for higher temperatures or heavier fits, while C2 is smaller than normal, used in applications needing minimal play.
• Cage - Pressed steel cages are the standard, robust choice. Whereas polyamide cages run quietly and resist wear, they have temperature limits, typically around 120°C for continuous use. 
• Environmental and material - Use stainless steel for moisture or corrosion, hybrid or insulated bearings where electrical current could pass through the bearing, and high-temperature greases and seals for hot environments.

Essential references and specialised ranges

How the numbering works:

The first digit, 6. Identifies a single-row deep groove ball bearing.

The next digit or digits indicate the dimension series: 618 and 619 are thin-section series, 60 is extra light, 62 is light, 63 is medium, and 64 is heavy.

The last two digits indicate the bore:

00 = 10mm, 01 = 12mm, 02 = 15mm, 03 = 17mm

From 04 upwards, multiply by five (for example, 05 = 25mm and 10 = 50mm)

For bores under 10mm, the last digit is the bore itself, so a 608 has an 8mm bore.

Click here to see our bearing size chart

Suffixes:

Z = metal shield on one side

ZZ, 2Z = metal shields on both sides

RS, LU, DU, RSR = rubber contact seal on one side

2RS, 2RS1, 2RSH, 2RSR, DDU, LLU = rubber contact seals on both sides

FAQ - All you need to know about deep groove ball bearings

Why are they called “deep groove” bearings?

The raceways are machined as deep, continuous grooves that closely match the curvature of the balls. This close fit, along with the uninterrupted raceways, is what allows the bearing to support axial loads in both directions as well as radial loads.

Can they tolerate misalignment?

Only to a very small degree, typically just a few minutes of arc, depending on clearance and load. Excessive misalignment increases noise, heat, and wear, so shafts and housings should be accurately aligned.

What is the difference between 2RS and ZZ?

2RS bearings have rubber contact seals that protect better against dust and moisture, but they create more friction and usually have a lower limiting speed. ZZ bearings have non-contact metal shields that create less friction and allow higher speeds, but they protect less well against fine particles and liquids.

Click here to learn how to replace rubber seals or metal shields on bearings.

Do deep groove ball bearings need lubrication?

Yes, lubrication separates the balls from the raceways, reduces friction, and protects against corrosion. Sealed and shielded bearings are supplied pre-greased and are usually intended to be replaced rather than lubricated.

Click here to learn how to maintain a bearing.

Can I replace a deep groove ball bearing myself?

In many cases, yes, using a bearing puller for removal and a press or fitting tool for installation. Apply force only to the ring that is being press-fitted (usually the inner ring onto a shaft), never through the balls. Never strike the bearing directly with a hammer, as this can dent the raceways and greatly shorten its life. 

How do I identify a bearing I need to replace?

The reference is usually marked on the shield, seal, or side face of the rings. If the markings are worn away, measure the bore, outer diameter, and width with callipers and match them against a size chart. Also note whether the bearing is open, shielded, or sealed.

Click here to learn how to measure a bearing.

How can I tell if a bearing is worn or failing?

Warning signs include:

• Grinding, rumbling, or clicking noises
• Increased vibration
• Rough or uneven rotation when the bearing is turned by hand
• Play in the shaft
• Overheating
• Grease leaking from the seals

Click here to learn how to recognise a failing bearing and tips on how to extend the life of bearings.