61921 bearing: complete specifications & equivalents
The 61921 is a ISO 15 radial bearing sized 105 x 145 x 20 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 | 145 mm |
| Width B | 20 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 | 44.2 kN |
| Basic static load rating C0 | 44 kN |
| Fatigue load limit Pu | 1.7 kN |
| Reference speed (thermal) | 9500 rpm |
| Limiting speed (mechanical) | 5600 rpm |
| Operating temperature | -40 to +150 °C |
| Mass | 870 g |
| Manufacturer designation | SKF 61921 |
| Standard | ISO 15 |
| Catalog version | SKF PUB BU/P1 17000/1 EN (Oct 2018) |
| Last verified | 2026-09-25 |
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 & 61900-series range
| Bore d | 4.134 in |
|---|---|
| Outer diameter D | 5.709 in |
| Width B | 0.787 in |
| ISO bore code | 21 |
| Radial section height (D−d)/2 | 20 mm |
| Smallest bore in 61900-series | 3 mm |
| Largest outer diameter in 61900-series | 1120 mm |
| Width range across 61900-series | 3–118 mm |
| Bore position in 61900-series (smallest first) | 29 of 63 |
| Bore above smallest 61900-series size | 102 mm |
Cross references & equivalents
| Equivalent model | Brand | Match level | Note |
|---|---|---|---|
| 61921-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. |
| 61921-RSR | NSK | partial Main dimensions match; tolerances, seals or internal clearance differ. | Same 105×145×20 mm envelope per ISO 15; seal variant differs (OPEN vs RSR) — confirm sealing suits the duty. |
| 61921-ZZ | NSK | partial Main dimensions match; tolerances, seals or internal clearance differ. | Same 105×145×20 mm envelope per ISO 15; seal variant differs (OPEN vs ZZ) — confirm sealing suits the duty. |
| 61921-2RS | NTN | partial Main dimensions match; tolerances, seals or internal clearance differ. | Same 105×145×20 mm envelope per ISO 15; seal variant differs (OPEN vs 2RS) — confirm sealing suits the duty. |
| 61921-NTN | NTN | 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. |
| 61921-RSR-NTN | NTN | partial Main dimensions match; tolerances, seals or internal clearance differ. | Same 105×145×20 mm envelope per ISO 15; seal variant differs (OPEN vs RSR) — confirm sealing suits the duty. |
| 61921-ZZ-NTN | NTN | partial Main dimensions match; tolerances, seals or internal clearance differ. | Same 105×145×20 mm envelope per ISO 15; seal variant differs (OPEN vs ZZ) — confirm sealing suits the duty. |
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 61921 model number is decoded
61921 is supplied open, without shields or seals, so the arrangement around it must supply and retain the lubricant. Within the thin 619xx section (diameter series 9 of ISO 15), multiplying bore code 21 by five gives the 105 mm bore; the 145 mm outside diameter and 20 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. 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
- clutch and transmission assemblies
- robotics and automation joints
- lay shafts and idler shafts
- textile machinery
Known failure patterns
- contamination wear from dust and dirt ingress through the open arrangement
- lubricant starvation when no regreasing interval is maintained
- 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 619xx thin section at 105 mm bore (20.0 mm section height) cannot shrug off the misalignment a standard section tolerates; keep the housing bores round and aligned, or edge contact will spall the raceways early.
- The open 61921 has no lubricant retention: grease escapes and contaminants migrate straight into the 105×145×20 mm raceway, so specify a sealed arrangement for dusty or washdown duty.
- Open bearings tolerate the highest speeds in the 61900-series but need a defined regreasing interval; run-to-failure lubrication is the dominant cause of early failure in open 61921 units.
- Do not quieten a noisy bearing by preloading it: the 61900-series is a deep-groove design, not angular-contact; axial preload raises temperature and shortens grease life.
- Vibration during standstill brinells the raceways of a 105 mm bearing at ball spacing; if the machine sits idle next to running equipment, turn the shaft over periodically or isolate the arrangement.
- The open 61921 needs external sealing and application-supplied lubrication; in the SKF catalogue the protected variants are separate order numbers 61921-2Z (shields) and 61921-2RSH (contact seals), not suffix-free 61921.
- The 44.2/44 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 61921 bearing?
A 61921 deep-groove ball bearing has a 105 mm bore, 145 mm outer diameter and 20 mm width (4.134 × 5.709 × 0.787 in), per ISO 15 boundary dimensions. It is an open bearing with no seals or shields.
What lubrication does 61921 need?
The open 61921 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 61921 bore code work?
The last two digits of 61921 are bore code 21, giving 21 × 5 = 105 mm bore. The 145 mm outside diameter and 20 mm width follow the ISO 15 diameter series, not the bore code alone.
What does no suffix on 61921 mean?
A bare 61921 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 61921?
In the SKF Rolling Bearings catalogue this size is listed as 61921 — the open (unsealed) execution, 105×145×20 mm per ISO 15. Quoted values: C 44.2 kN, C0 44 kN, Pu 1.7 kN, limiting speed 5600 r/min, mass 870 g. Brand suffixes (2Z, 2RSH, 2RSL) differ from the industry-neutral spelling 61921.
Reviewed & verified by the MPN Base engineering desk against source catalog SKF PUB BU/P1 17000/1 EN (Oct 2018) on 2026-09-25. Read our editorial & correction policy.