6304 Bearing Dimensions and Replacement Selection Guide
A 6304 replacement should be selected by its full designation and operating requirements. This guide explains what to compare and includes supplier search links. Brand rankings, star scores and service-life promises are not supported by comparative test data here.
6304 Dimensions at a Glance
| Specification | Value |
|---|---|
| Bore (inner diameter) | 20 mm (0.7874 in) |
| Outer diameter | 52 mm (2.0472 in) |
| Width | 15 mm (0.5906 in) |
Weight, load ratings and speed limits are specific to the manufacturer and full variant. They are not universal properties of the base number 6304. Check the current data sheet for the exact suffix before using those values in a design.
What Does 6304 Mean?
The 6304 designation follows the ISO size standard: 6 is a single-row deep groove ball type, 3 is the medium series, and 04 means a 20mm bore diameter.
The 6304 is a step up from the 6204 in load capacity while sharing the same 20mm bore.
Common Applications
- Electric motors (small to medium duty)
- Automotive water pumps and alternators
- HVAC blower motors
- Small gearboxes and speed reducers
- Power tools (drills, angle grinders)
- Agricultural equipment
- Industrial pumps
Compare the Exact 6304 Variant
This guide does not rank brands by tested performance. Price, life, noise and speed depend on the exact bearing variant and application. Compare a current manufacturer data sheet and a traceable supplier quote before ordering.
- Dimensions: match bore, outside diameter and width.
- Construction: match seals or shields, internal clearance, cage and tolerance class.
- Operating limits: check the exact variant’s load ratings, permissible speed, lubricant and temperature range.
- Supply: verify the full designation, seller identity, packaging and purchase documentation.
Supplier Search Links
These affiliate links are starting points for checking availability. Search results can include different suffixes and sellers; they are not verified equivalents or authenticity guarantees.
SKF 6304
→ Check SKF 6304 price on Amazon
NSK 6304
→ Check NSK 6304 price on Amazon
NTN 6304
→ Check NTN 6304 price on Amazon
Timken 6304
→ Check Timken 6304 price on Amazon
FAG 6304
→ Check FAG 6304 price on Amazon
Koyo 6304
→ Check Koyo 6304 price on Amazon
6304 Seal Types Explained
- 6304 (open) — no seal, needs external lubrication.
- 6304 Z / ZZ — metal shields (one or both sides). Dust protection.
- 6304 RS / 2RS — rubber contact seals. Best for wet or dirty environments.
- 6304 ZZ C3 — internal clearance C3, common in electric motors.
Match the closure and internal clearance specified for the machine. A sealed variant is not automatically the correct replacement for a shielded or open one.
6304 vs Related Sizes
| Size | Bore | OD | Width |
|---|---|---|---|
| 6204 | 20 mm | 47 mm | 14 mm |
| 6304 (this page) | 20 mm | 52 mm | 15 mm |
| 6305 | 25 mm | 62 mm | 17 mm |
| 6404 | 20 mm | 72 mm | 19 mm |
Frequently Asked Questions
What is the difference between 6304 and 6204?
Both have a 20mm bore, but the 6304 has a larger 52mm outer diameter versus the 6204’s 47mm, and a 15mm width versus 14mm. Compare load ratings for the exact manufacturer and variant; boundary dimensions alone do not establish a fixed percentage increase.
Can I substitute a 6304 ZZ for a 6304 2RS?
Matching dimensions is insufficient. Check the machine’s sealing, lubrication, speed, clearance and temperature requirements before substituting a shielded bearing for a contact-sealed one.
What is the max RPM of a 6304?
There is no single maximum RPM for every 6304. Seals, cage, lubricant, load and temperature affect permissible speed. Use the exact variant’s manufacturer data and application guidance; reference speed and limiting speed are different ratings.
How do I identify a genuine SKF or NSK 6304?
Markings and appearance alone cannot establish authenticity. Buy from a distributor listed by the manufacturer, keep purchase documentation, and use the manufacturer’s verification service if a product is in doubt.
Which 6304 brand lasts longest?
No fixed winner or service life can be established from the brand name alone. Bearing fatigue life depends on load and speed, while lubrication, contamination and mounting can cause earlier failure. NSK’s explanation of dynamic load ratings and fatigue life describes L10 life as a statistical rating, not a guarantee for an individual bearing.