6321 bearing: complete specifications & equivalents
The 6321 is a ISO 15 radial bearing sized 105 x 225 x 49 mm (bore x OD x width). 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 | open |
| 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) | 4000 rpm |
| Operating temperature | -40 to +150 °C |
| Mass | 8200 g |
| Manufacturer designation | SKF 6321 |
| 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 (OPEN vs 2RS) — confirm sealing suits the duty. |
| 6321-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-ZZ-NSK | NSK | partial Main dimensions match; tolerances, seals or internal clearance differ. | Same 105×225×49 mm envelope per ISO 15; seal variant differs (OPEN vs ZZ) — confirm sealing suits the duty. |
| 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 (OPEN 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; catalogue load ratings differ by >10% — re-rate the application 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; seal variant (OPEN vs ZZ) and load ratings differ — confirm sealing and rating 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 model number is decoded
In the 6300-series (diameter series 3 of ISO 15) the last two digits encode the bore: 6321 carries bore code 21 = 105 mm. Outside diameter 225 mm and width 49 mm come from the ISO 15 boundary-dimensions general plan. With no seal suffix the bearing is open: no shields or seals are fitted and lubrication is supplied by the application. For normal-load mounting with a rotating inner ring on a 105 mm shaft, typical catalogue practice is a m6 shaft seat with an H7 housing bore — verify against the actual load direction and magnitude. In the SKF catalogue this open execution carries the bare designation; protected variants are ordered separately as -2Z and -2RSH.
Typical equipment & failure modes
Common applications
- hoists and winches
- heavy conveyors
- pulp and paper machinery
- medium and heavy industrial drives
Known failure patterns
- contamination wear from dust and dirt ingress through the open arrangement
- lubricant starvation when no regreasing interval is maintained
- brinelling from static overload or hammering during mounting
- false brinelling from vibration while the shaft is stationary
Selection pitfalls — read before you substitute
- At 105 mm bore the ring mass is significant: heat 6321 on an induction heater (max 120 °C), never over an open flame, and plan puller access or a withdrawal sleeve now for the day it has to come off again.
- 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.
- Storage matters for open bearings: 6321 leaves the factory with rust preventive only, so clean it and apply the service grease at assembly even if the rings look oily from the wrapper.
- Open bearings tolerate the highest speeds in the 6300-series but need a defined regreasing interval; run-to-failure lubrication is the dominant cause of early failure in open 6321 units.
- Deep-groove ball bearings tolerate only minutes of misalignment; if the 225 mm housing cannot be aligned, switch to a self-aligning type rather than shimming 6321.
- The housing bore for the 225 mm OD should be round within IT7; an oval bore pinches the outer ring of 6321 and shows up later as two-point loaded raceway wear.
- The open 6321 needs external sealing and application-supplied lubrication; in the SKF catalogue the protected variants are separate order numbers 6321-2Z (shields) and 6321-2RSH (contact seals), not suffix-free 6321.
- 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 bearing?
A 6321 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 an open bearing with no seals or shields.
What lubrication does 6321 need?
The open 6321 is lubricated by the application; a NLGI 2 lithium-soap grease filled to roughly 25–35% of the free volume is the common choice, with a defined relubrication interval.
How does the 6321 bore code work?
The last two digits of 6321 are bore code 21, giving 21 × 5 = 105 mm bore. The 225 mm outside diameter and 49 mm width follow the ISO 15 diameter series, not the bore code alone.
What does no suffix on 6321 mean?
A bare 6321 designation means open: no shields or seals, normal CN radial clearance and P0 normal tolerance unless further suffixes are ordered. The application must supply and retain the lubrication.
What is the SKF designation and catalogue data for 6321?
In the SKF Rolling Bearings catalogue this size is listed as 6321 — the open (unsealed) execution, 105×225×49 mm per ISO 15. Quoted values: C 182 kN, C0 153 kN, Pu 5.1 kN, limiting speed 4000 r/min, mass 8200 g. Brand suffixes (2Z, 2RSH, 2RSL) differ from the industry-neutral spelling 6321.
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.