6321-ZZ bearing: complete specifications & equivalents
The 6321-ZZ is a ISO 15 radial bearing sized 105 x 225 x 49 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 | 105 mm |
| Outer diameter D | 225 mm |
| Width B | 49 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 | 182 kN |
| Basic static load rating C0 | 153 kN |
| Fatigue load limit Pu | 5.1 kN |
| Reference speed (thermal) | 6300 rpm |
| Limiting speed (mechanical) | 3200 rpm |
| Operating temperature | -30 to +120 °C |
| Mass | 8250 g |
| Manufacturer designation | SKF 6321-2Z |
| 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 | 4.134 in |
|---|---|
| Outer diameter D | 8.858 in |
| Width B | 1.929 in |
| ISO bore code | 21 |
| Radial section height (D−d)/2 | 60 mm |
| Smallest bore in 6300-series | 2 mm |
| Largest outer diameter in 6300-series | 500 mm |
| Width range across 6300-series | 3–95 mm |
| Bore position in 6300-series (smallest first) | 28 of 40 |
| Bore above smallest 6300-series size | 103 mm |
Cross references & equivalents
| Equivalent model | Brand | Match level | Note |
|---|---|---|---|
| 6321-2RS | NSK | partial Main dimensions match; tolerances, seals or internal clearance differ. | Same 105×225×49 mm envelope per ISO 15; seal variant differs (ZZ vs 2RS) — confirm sealing suits the duty. |
| 6321-NSK | NSK | partial Main dimensions match; tolerances, seals or internal clearance differ. | Same 105×225×49 mm envelope per ISO 15; seal variant differs (ZZ vs OPEN) — confirm sealing suits the duty. |
| 6321-ZZ-NSK | NSK | full Dimensions and internal design equivalent — standard interchange. | Identical ISO 15 envelope, seal and ratings band — standard interchange; re-verify precision class and clearance per supplier. |
| 6321-2RS-NTN | NTN | partial Main dimensions match; tolerances, seals or internal clearance differ. | Same 105×225×49 mm envelope per ISO 15; seal variant (ZZ vs 2RS) and load ratings differ — confirm sealing and rating before substituting. |
| 6321-NTN | NTN | partial Main dimensions match; tolerances, seals or internal clearance differ. | Same 105×225×49 mm envelope per ISO 15; seal variant (ZZ vs OPEN) and load ratings differ — confirm sealing and rating before substituting. |
| 6321-ZZ-NTN | NTN | partial Main dimensions match; tolerances, seals or internal clearance differ. | Same 105×225×49 mm envelope per ISO 15; catalogue load ratings differ by >10% — re-rate the application before substituting. |
| 7321 | SKF | verify Commonly quoted cross reference; confirm against the target catalog before ordering. | — |
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 6321-ZZ model number is decoded
6321-ZZ carries two non-contact sheet-steel shields that hold the factory grease in and keep coarse debris out; they do not seal against liquids. Within the medium 63xx section (diameter series 3 of ISO 15), multiplying bore code 21 by five gives the 105 mm bore; the 225 mm outside diameter and 49 mm width follow the same boundary-dimension plan. For a rotating inner ring on a 105 mm shaft under normal load, catalogue practice seats it on a m6 shaft fit with an H7 housing bore — confirm against the actual load direction and magnitude before committing. SKF's own suffix is 2Z (this page's industry-neutral spelling is -ZZ); catalogue number 6321-2Z.
Typical equipment & failure modes
Common applications
- hoists and winches
- heavy conveyors
- pulp and paper machinery
- medium and heavy industrial drives
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
- electrical pitting in VFD-driven motors without grounding protection
- raceway smearing under marginal lubrication at start-up
Selection pitfalls — read before you substitute
- Mount this 105 mm bore bearing by heating the inner ring (induction heater, max 120 °C) — never drive it home through the outer ring or balls, that brinells the raceways.
- The 63xx medium series gains rating at 105 mm bore through a 225 mm OD and 49 mm width; the heavier rolling elements also trade away some speed versus a 6221.
- Do not wash 6321-ZZ in solvent before mounting: the grease inside the shielded cavity is the service fill, and solvent creeping past the shield gap strips it out.
- Shielded 6321-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.
- Measure the shaft, do not trust the drawing: a 105 mm nominal journal worn by even 0.02 mm turns an interference seat into a creeping fit that frets the bore of 6321-ZZ.
- Grease compatibility is not guaranteed between fills: mixing lithium and polyurea thickeners in a 6300-series position can soften the mixture and leak — clean out the old fill before switching grease types.
- SKF spells the shielded version 6321-2Z (one shield: 6321-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 6321-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 6321-2Z for high-contamination positions.
- The 182/153 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 6321-ZZ bearing?
A 6321-ZZ deep-groove ball bearing has a 105 mm bore, 225 mm outer diameter and 49 mm width (4.134 × 8.858 × 1.929 in), per ISO 15 boundary dimensions. It is fitted with two non-contact metallic shields.
What does the ZZ suffix on 6321-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 105 mm bore?
The '3' is the medium diameter series: 225×49 mm, 60.0 mm radial section at 105 mm bore, carrying more load than a 6221 but needing a larger housing bore and giving up some speed.
Are 6321 bearings from different brands interchangeable?
For boundary dimensions, yes: every brand's 6321 uses the same ISO 15 envelope (105×225×49 mm). Load ratings, limiting speeds, clearance, precision class and sealing design can differ, so verify those in the supplier catalogue when substituting. Seal suffixes also differ by brand (2RS, DDU, LLU, 2RSL and similar).
What is the SKF designation and catalogue data for 6321-ZZ?
In the SKF Rolling Bearings catalogue this size is listed as 6321-2Z — two non-contact sheet-metal shields, 105×225×49 mm per ISO 15. Quoted values: C 182 kN, C0 153 kN, Pu 5.1 kN, limiting speed 3200 r/min, mass 8250 g. Brand suffixes (2Z, 2RSH, 2RSL) differ from the industry-neutral spelling 6321-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.