6304-ZZ bearing: complete specifications & equivalents
The 6304-ZZ is a ISO 15 radial bearing sized 20 x 52 x 15 mm (bore x OD x width) with ZZ sealing. Verify dimensions against the official catalog before ordering.
Specification table
| Parameter | Value |
|---|---|
| Bore diameter d | 20 mm |
| Outer diameter D | 52 mm |
| Width B | 15 mm |
| Material | GCr15 |
| Seal / shield | ZZ |
| Internal clearance | CN / C3 available |
| Tolerance class | P0 |
| Cage | steel, stamped ribbon (J-type) |
| Basic dynamic load rating C | 16.8 kN |
| Basic static load rating C0 | 7.8 kN |
| Fatigue load limit Pu | 0.335 kN |
| Reference speed (thermal) | 30000 rpm |
| Limiting speed (mechanical) | 15000 rpm |
| Operating temperature | -30 to +120 °C |
| Mass | 150 g |
| Manufacturer designation | SKF 6304-2Z |
| Standard | ISO 15 |
| Catalog version | SKF PUB BU/P1 17000/1 EN (Oct 2018) |
| Last verified | 2026-09-24 |
Source: catalog reference (SKF PUB BU/P1 17000/1 EN (Oct 2018)) · extracted 2026-09-24
Parameters extracted from the official SKF Rolling Bearings catalogue (SKF PUB BU/P1 17000/1 EN (Oct 2018)); SKF® and SKF Explorer® are trademarks of AB SKF, used here for identification only — mpnbase is not an authorized SKF distributor. Boundary dimensions are ISO 15 interchangeable; current production values may differ, verify at skf.com.
Dimensions in inches & 6300-series range
| Bore d | 0.787 in |
|---|---|
| Outer diameter D | 2.047 in |
| Width B | 0.591 in |
| ISO bore code | 04 |
| Radial section height (D−d)/2 | 16 mm |
| Smallest bore in 6300-series | 10 mm |
| Largest outer diameter in 6300-series | 400 mm |
| Width range across 6300-series | 11–78 mm |
| Bore position in 6300-series (smallest first) | 5 of 30 |
| Bore above smallest 6300-series size | 10 mm |
Cross references & equivalents
| Equivalent model | Brand | Match level | Note |
|---|---|---|---|
| 6304 | ISO 15 | verify Commonly quoted cross reference; confirm against the target catalog before ordering. | ISO 15 boundary-dimension envelope; seal suffix convention varies by brand (2RS / DDU / LLU / 2RSR) — verify seal design and temperature range. Brand-specific OEM equivalents pending multi-source data. |
Interchange levels: full standard interchange · partial verify parameters · verify manual confirmation required. Links resolve to the equivalent model's specification page where available.
How the 6304-ZZ model number is decoded
In the 6300-series (ISO 15 diameter series 3) the last two digits encode the bore: 6304 carries bore code 04 = 20 mm. Outside diameter 52 mm and width 15 mm come from the ISO 15 boundary-dimensions general plan. Suffix -ZZ denotes two non-contact metallic shields; they retain grease and block coarse debris but are not liquid-tight. For normal-load mounting with a rotating inner ring on a 20 mm shaft, typical catalogue practice is a k5 shaft seat with an H7 housing bore — verify against the actual load direction and magnitude. SKF's own suffix is 2Z (this page's industry-neutral spelling is -ZZ); catalogue number 6304-2Z.
Typical equipment & failure modes
Common applications
- small gearboxes
- conveyors and drives
- agricultural equipment
- fans and blowers
Known failure patterns
- fine-particle abrasion when non-contact shields let dust past in dirty duty
- grease aging in the shield-for-life cavity with no relubrication path
- brinelling from static overload or hammering during mounting
- false brinelling from vibration while the shaft is stationary
Selection pitfalls — read before you substitute
- At a 20 mm bore, a shaft-seat burr or an overtight setscrew can score the thin inner ring of 6304-ZZ; check shaft finish and runout (target Ra ≤ 1.6 µm) before pressing it home.
- The 63xx medium series gains rating at 20 mm bore through a 52 mm OD and 15 mm width; the heavier rolling elements also trade away some speed versus a 6204.
- ZZ shields are non-contact: 6304-ZZ blocks chips and coarse dust but is not waterproof — do not install it expecting a pressure-wash seal, step up to 6304-2RS for that.
- Shielded 6304-ZZ units are typically greased for life; prying the shields out for regreasing usually bends them and leaves a gap that throws grease in service.
- Deep-groove ball bearings tolerate only minutes of misalignment; if the 52 mm housing cannot be aligned, switch to a self-aligning type rather than shimming 6304-ZZ.
- SKF spells the shielded version 6304-2Z (one shield: 6304-Z), not "-ZZ": the suffix language differs by brand even though the ISO envelope is identical, so quote the brand designation when ordering.
- The single-shield execution 6304-Z is a distinct order number in catalogue 17000: it suits open gears or oil-bath arrangements where the unshielded face faces the lubricant, and it is not interchangeable with the double-shield 6304-2Z for high-contamination positions.
- The 16.8/7.8 kN ratings here are SKF Explorer-class figures from catalogue PUB BU/P1 17000/1 EN (Oct 2018); SKF can revise internal geometry and ratings without changing the designation, so treat the catalogue version and date as part of the specification and re-verify for critical drives.
Frequently asked questions
What are the dimensions of a 6304-ZZ bearing?
A 6304-ZZ deep-groove ball bearing has a 20 mm bore, 52 mm outer diameter and 15 mm width (0.787 × 2.047 × 0.591 in), per ISO 15 boundary dimensions. It is fitted with two non-contact metallic shields. Geometry-based estimated mass is about 138 g for a steel-cage unit; catalogue masses vary slightly with seal and cage design.
How does the 6304 bore code work?
The last two digits of 6304 are bore code 04, giving 04 × 5 = 20 mm bore. The 52 mm outside diameter and 15 mm width follow the ISO 15 diameter series, not the bore code alone.
What does the ZZ suffix on 6304-ZZ mean?
ZZ means two non-contact sheet-metal shields, one each side. They retain factory grease and block coarse particles with little friction, but do not seal against liquids, fine dust or pressure washing.
How does the 6300 compare with other series at the same 20 mm bore?
The '3' is the medium diameter series: 52×15 mm, 16.0 mm radial section at 20 mm bore, carrying more load than a 6204 but needing a larger housing bore and giving up some speed.
What is the SKF designation and catalogue data for 6304-ZZ?
In the SKF Rolling Bearings catalogue this size is listed as 6304-2Z — two non-contact sheet-metal shields, 20×52×15 mm per ISO 15. Quoted values: C 16.8 kN, C0 7.8 kN, Pu 0.335 kN, limiting speed 15000 r/min, mass 150 g. Brand suffixes (2Z, 2RSH) differ from the industry-neutral spelling 6304-ZZ.
Reviewed & verified by the MPN Base engineering desk against source catalog SKF PUB BU/P1 17000/1 EN (Oct 2018) on 2026-09-24. Read our editorial & correction policy.