306-ZZ bearing: complete specifications & equivalents
The 306-ZZ is a ISO 15 radial bearing sized 30 x 72 x 19 mm (bore x OD x width) with ZZ sealing. Verify dimensions against the official catalog before ordering.
Specification table
| Parameter | Value |
|---|---|
| Brand | SKF |
| Bore diameter d | 30 mm |
| Outer diameter D | 72 mm |
| Width B | 19 mm |
| Material | GCr15 |
| Seal / shield | ZZ |
| Internal clearance | CN |
| Tolerance class | P0 |
| Cage | steel, stamped ribbon (J-type) |
| Basic dynamic load rating C | 29.7 kN |
| Basic static load rating C0 | 21.6 kN |
| Fatigue load limit Pu | 0.93 kN |
| Reference speed (thermal) | 18000 rpm |
| Limiting speed (mechanical) | 8800 rpm |
| Operating temperature | -40 to +120 °C |
| Mass | 370 g |
| Manufacturer designation | 306-2Z |
| Standard | ISO 15 |
| Catalog version | SKF PUB BU/P1 17000/1 EN (Oct 2018) |
| Last verified | 2026-09-27 |
Source: catalog reference (SKF PUB BU/P1 17000/1 EN (Oct 2018)) · extracted 2026-09-27
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 & 300-series range
| Bore d | 1.181 in |
|---|---|
| Outer diameter D | 2.835 in |
| Width B | 0.748 in |
| ISO bore code | 06 |
| Radial section height (D−d)/2 | 21 mm |
| Smallest bore in 300-series | 25 mm |
| Largest outer diameter in 300-series | 190 mm |
| Width range across 300-series | 17–43 mm |
| Bore position in 300-series (smallest first) | 2 of 14 |
| Bore above smallest 300-series size | 5 mm |
Cross references & equivalents
| Equivalent model | Brand | Match level | Note |
|---|---|---|---|
| W6306-2RS | SKF | partial Main dimensions match; tolerances, seals or internal clearance differ. | Same 30×72×19 mm envelope, but the stainless and chrome-steel executions carry different catalogue ratings (29.7/21.6 kN vs 22.9/15 kN) — envelope match, not a load-rating equivalent; choose by corrosion versus load duty. |
| W6306-ZZ | SKF | partial Main dimensions match; tolerances, seals or internal clearance differ. | Same 30×72×19 mm envelope, but the stainless and chrome-steel executions carry different catalogue ratings (29.7/21.6 kN vs 22.9/15 kN) — envelope match, not a load-rating equivalent; choose by corrosion versus load duty. |
| W6306 | SKF | partial Main dimensions match; tolerances, seals or internal clearance differ. | Same 30×72×19 mm envelope, but the stainless and chrome-steel executions carry different catalogue ratings (29.7/21.6 kN vs 22.9/15 kN) — envelope match, not a load-rating equivalent; choose by corrosion versus load duty. |
| 306 | SKF | full Dimensions and internal design equivalent — standard interchange. | Same 30×72×19 mm envelope and equivalent catalogue ratings; 306 is the open arrangement execution of this size — boundary dimensions interchangeable, only the seal/shield/cage execution differs. |
| 6306 | SKF | partial Main dimensions match; tolerances, seals or internal clearance differ. | SKF SKF 6306 shares the 30×72×19 mm envelope but catalogue C/C0 differ (29.7/21.6 kN vs 29.6/16 kN) — envelope match, not a load-rating equivalent. |
| 6306-ZZ | SKF | partial Main dimensions match; tolerances, seals or internal clearance differ. | SKF SKF 6306-2Z shares the 30×72×19 mm envelope but catalogue C/C0 differ (29.7/21.6 kN vs 29.6/16 kN) — envelope match, not a load-rating equivalent. |
| 6306-2RS | SKF | partial Main dimensions match; tolerances, seals or internal clearance differ. | SKF SKF 6306-2RSH shares the 30×72×19 mm envelope but catalogue C/C0 differ (29.7/21.6 kN vs 29.6/16 kN) — envelope match, not a load-rating equivalent. |
| 6306-RSR | SKF | partial Main dimensions match; tolerances, seals or internal clearance differ. | SKF SKF 6306-2RZ shares the 30×72×19 mm envelope but catalogue C/C0 differ (29.7/21.6 kN vs 29.6/16 kN) — envelope match, not a load-rating equivalent. |
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 306-ZZ model number is decoded
306-2Z is a filling-slot (notched-ring) deep-groove bearing in the legacy 300-series: the last two digits encode the bore: 306 carries code 06 = 30 mm (code × 5). The rings carry loading slots that allow extra balls during assembly, which is what gives the 30×72×19 mm envelope its C 29.7 kN and C0 21.6 kN ratings (Pu 0.93 kN). SKF spells the double shield 306-2Z (suffix 2Z); the shields are non-contact, retain grease and block coarse debris but are not liquid-tight. Limiting speed 8800 r/min, mass 370 g. These bearings are built for high purely-radial loads at moderate speeds.
Typical equipment & failure modes
Common applications
- slow heavy gearboxes
- farm machinery and harvesters
- construction equipment drives
- hoists and winch gear trains
Known failure patterns
- spalling of the filling-slot edge when balls are hammered through the slot under heavy thrust loading
- dirt entering through the open slot area when external sealing is neglected
- brinelling from static overload or hammer blows during mounting
- false brinelling from vibration while the shaft stands idle
Selection pitfalls — read before you substitute
- Limiting speed is just 8800 r/min: filling-slot cages and the slot geometry run cooler below that — overspeed drives cage wear and smearing.
- Filling slots let more balls be packed into the 30×72 mm envelope, which is why 306-ZZ reaches C 29.7 kN — but the slots also mean the two rings separate when the balls align with them, so handle it as a loose-clearance design.
- The slots sit at one angular position: on 306-ZZ, never pass the full radial load across the slot zone during mounting or the ring lip can crack.
- 306 uses the legacy SKF 200/300 numbering (light/heavy filling-slot series), not the modern 6200/6300 spelling; quote 306-2Z exactly when ordering replacements.
- The slots sit at one angular position: on 306-ZZ, never pass the full radial load across the slot zone during mounting or the ring lip can crack.
- Mount by heating the inner ring (max 120 °C) — driving 306-ZZ home through the outer ring or balls brinells the raceways.
Frequently asked questions
What are the dimensions of 306-ZZ?
Filling-slot bearing 306-2Z measures 30×72×19 mm (1.181×2.835×0.748 in), about 370 g.
What does the designation 306 mean?
It is the legacy 200/300 filling-slot numbering: series 300 and bore code 06 = 30 mm. Filling-slot bearings predate the 6xxx deep-groove spelling.
What fails on 306-ZZ?
Slot-edge chipping under thrust or shock, dirt ingress in the open design and cage wear past the 8800 r/min limiting speed are the typical failure modes.
Is 306-ZZ available sealed?
Shielded executions (-2Z, listed here as 306-ZZ) exist; contact-sealed versions are generally not produced for the filling-slot family.
Reviewed & verified by the MPN Base engineering desk against source catalog SKF PUB BU/P1 17000/1 EN (Oct 2018) on 2026-09-27. Read our editorial & correction policy.