The 6304 is a widely used single-row deep-groove ball bearing known for its compact dimensions, robust construction, and versatility. Its standard metric size is 20 mm (ID) × 52 mm (OD) × 15 mm (width). The 6304 is available in open, shielded (ZZ) and sealed (2RS) versions and suits a broad range of electric motors, pumps, gearboxes, conveyors and household appliances.
1. 6304 Bearing — Description
The 6304 belongs to the 6300 series of single-row deep-groove ball bearings. These bearings have continuous raceway grooves in both inner and outer rings that allow them to carry primarily radial loads and moderate axial loads in both directions. Deep-groove ball bearings are valued for low friction, quiet running, and high-speed capability when correctly lubricated. The 6304 is produced to standardized dimensions, making it easy to cross-reference between manufacturers and suppliers. It is available in different internal clearance grades, tolerance classes, and quality levels to satisfy a wide range of industrial and consumer requirements.
Key specifications (copy/paste ready):
Bore (d): 20 mm
Outer diameter (D): 52 mm
Width (B): 15 mm
Closure: Open
Material: Chrome steel (SAE 52100); stainless or hybrid options available on request
Internal clearance: Standard (C3 available on request)
Dynamic load (typical): ~15.9 kN (approx.)
Static load (typical): ~7.9 kN (approx.)
Limiting speed (open, depending on lubrication & cage): higher than sealed types — application dependent
Cage: Pressed steel cage (standard); brass or polyamide on request
Weight (approx): 0.145 kg
2. What size is a 6304 bearing?
The standard metric dimensions for a 6304 deep-groove ball bearing are:
Bore (d): 20 mm
Outer diameter (D): 52 mm
Width (B): 15 mm
These dimensions remain constant whether the part is labeled 6304, 6304-2RS, 6304-ZZ, or 6304C3. That consistent sizing is why the 6304 is commonly used as a drop-in replacement across many designs.
3. 6304 Bearing — Typical material solutions
Common material options for 6304 bearings include:
Chrome bearing steel (e.g., SAE 52100 / bearing steel): The industry-standard material offering excellent hardness, fatigue resistance and load capacity. Most mass-produced 6304 bearings use chrome steel rings and balls.
Stainless steel (e.g., AISI 440C): Used for corrosion resistance in food equipment, outdoor machinery, and marine applications. Stainless options trade some load capacity for better environmental resistance.
Hybrid (ceramic balls + steel rings): Silicon nitride (Si₃N₄) balls combined with steel rings provide lower mass, higher speed capability, lower thermal growth and improved corrosion resistance in some environments — often chosen for high-speed or precision applications.
Coatings and surface treatments: For improved corrosion protection or specialty uses, bearings can receive zinc plating, black oxide, or polymer coatings.
Equally important as material choice is lubrication: sealed bearings arrive pre-lubricated; open and shielded bearings require an appropriate grease or oil chosen for operating speed, temperature and load.
4. 6304 Bearing — Sealing & shield types explained
Choosing the right closure influences contamination protection, friction and service life. Typical closure types are:
6304 Open (no suffix): No seals or shields; best for high-speed or precision applications where the surrounding assembly provides sealing and lubrication. Offers the lowest friction.
6304ZZ / 6304-2Z (metal shields): Thin metal shields on one or both sides that provide protection from large particles while still allowing some grease exchange. Shields produce lower friction than rubber seals and suit many industrial uses.
6304-2RS / 2RSH / 2RSR (rubber contact seals): Elastomeric contact seals on both sides that keep out moisture and fine contaminants while retaining grease. These sealed bearings have slightly higher running friction and a lower maximum speed than ZZ-shielded versions but are preferred for wet or dusty environments.
Manufacturer-specific suffixes (e.g., DDU): Variants with different lip profiles or contact pressures offer tailored sealing performance or lower torque depending on brand and design.
How to choose: If contamination, moisture or poor maintenance is likely, choose 2RS. If you need lower running torque and higher top speed while accepting less protection, choose ZZ. If external seals exist and you need the best possible speed and lowest torque, choose open.
5. What is a 6304 bearing used for?
The 6304’s balanced size and performance make it extremely adaptable. Common applications include:
Electric motors: Widely used for rotor support in small and medium motors, where high rpm and long life are required.
Pumps and compressors: Sealed 6304-2RS variants are often used where moisture or particulate ingress is expected.
Gearboxes and power transmission: Provide radial and light axial support for shafts in gearboxes, reducers and couplings.
Fans, blowers, conveyors: Robust and economical for continuous operation equipment.
Household appliances: Washing machines, dryers and other appliances use sealed, pre-greased 6304 bearings for quiet, long-lasting operation.
Automotive auxiliary systems: Some alternators, water pumps and accessory drive components employ 6304 bearings depending on OEM design.
Because 6304 bearings come in different tolerance, clearance and quality grades, they are used in both consumer products and demanding industrial machinery.
6. 6300 series size chart (quick reference)
Quick reference chart for the 6300 series (d × D × B in mm):
Series d (mm) D (mm) B (mm)
| 6300 | 10 | 35 | 11 |
| 6301 | 12 | 37 | 12 |
| 6302 | 15 | 42 | 13 |
| 6303 | 17 | 47 | 14 |
| 6304 | 20 | 52 | 15 |
| 6305 | 25 | 62 | 17 |
| 6306 | 30 | 72 | 19 |
| 6307 | 35 | 80 | 21 |
| 6308 | 40 | 90 | 23 |
| 6309 | 45 | 100 | 25 |
| 6310 | 50 | 110 | 27 |
Use this chart for quick cross-referencing and parts selection.
7. Inspection, installation & maintenance tips for 6304 bearings
Correct mounting: Apply force to the ring being fitted (press the inner ring onto the shaft or press the outer ring into the housing) to avoid ring distortion. Avoid hammering directly on the bearing.
Fit tolerances and clearance: Follow OEM recommendations for shaft and housing tolerances. Some applications require C3 internal clearance for thermal expansion or misalignment.
Lubrication: Sealed 2RS bearings come factory greased. For open or ZZ bearings, use a grease or oil that matches operating speed and temperature. Over-greasing causes heat; under-greasing shortens life.
Clean handling: Even tiny contamination drastically reduces bearing life — handle in clean conditions and use clean tools and gloves.
Monitoring: Watch for increased vibration, noise, or temperature as early warning signs of bearing fatigue or contamination. Replace bearings showing visible wear, pitting, or corrosion.
8. Buying guide — How to choose the right 6304 for your project
Determine closure type: Open, ZZ, or 2RS based on contamination risk and friction tolerance.
Pick material: Standard chrome steel for general use; stainless for corrosion resistance; hybrid for high-speed or precision needs.
Select tolerance & clearance: Choose appropriate quality (standard/EMQ/precision) and internal clearance (normal, C3, etc.) to match operating conditions.
Choose grease & fill (if open/ZZ): Match grease type and quantity to operating speed, temperature and load.
Confirm traceability: For critical equipment, source from reputable manufacturers and distributors to ensure quality and part traceability.
9. Common part numbers & cross references
Typical part name variations include: 6304, 6304-2RS, 6304-ZZ, 6304C3. Verify the d × D × B dimensions and confirm the suffix (seal/shield/clearance) before ordering to ensure the correct replacement.
Interchange Numbers:6304J1, 304K, 304, 304KS, 5972K119, 6304.
6304RS, 6304LLU, 6304LU, 6304LLB, 6304DDU, 6304VV, 6304.2RSJ1, 6304EE, 6304-2RU, 304PP, 304KSZZ, 6304-2NSL, 99304, 6L053, 5972K56, 6661K125, 6304-2NSE, 6304.2RSR, 6304UU
6304Z, 6304 2Z, 6304SS, 6304 ZZ, 6304.2ZJ1, 304KSFF, 304KDD, 77304, 6L036, 5972K351, 6661K65
10. Conclusion
The 6304 bearing (20×52×15 mm) is a reliable, widely available component suitable for a wide spectrum of industrial and consumer applications. Choose seal and material variants according to environmental exposure, required speed, and maintenance philosophy. BYWB Bearing stocks a range of 6304 configurations — from open precision bearings to sealed maintenance-free 6304-2RS units and shielded 6304-ZZ variants — so you can specify the exact version your equipment requires.
