21311 bearing: complete specifications & equivalents
The 21311 is a ISO 15 radial bearing sized 55 x 120 x 29 mm (bore x OD x width). Verify dimensions against the official catalog before ordering.
Specification table
| Parameter | Value |
|---|---|
| Bore diameter d | 55 mm |
| Outer diameter D | 120 mm |
| Width B | 29 mm |
| Seal / shield | open |
| Internal clearance | CN / C3 / C4 available |
| Tolerance class | P0 |
| Cage | steel |
| Operating temperature | -30 to +120 °C |
| Mass (geometry estimate) | 1322 g |
| Standard | ISO 15 |
| Catalog version | iso15-srb-geometry |
| Last verified | 2026-09-24 |
Source: ISO 15 boundary-dimensions standard · extracted 2026-09-24
Standard-interchange bearing: dimensions per ISO 15; CN clearance, P0 tolerance and a stamped-steel cage are catalogue defaults unless the supplier states otherwise, and mass is a geometry-derived estimate. Brand catalogue load ratings and limiting speeds for 21311 are being backfilled — use the inquiry form for certified values.
Dimensions in inches & 21300-series range
| Bore d | 2.165 in |
|---|---|
| Outer diameter D | 4.724 in |
| Width B | 1.142 in |
| ISO bore code | 11 |
| Radial section height (D−d)/2 | 32.5 mm |
| Smallest bore in 21300-series | 50 mm |
| Largest outer diameter in 21300-series | 240 mm |
| Width range across 21300-series | 27–50 mm |
| Bore position in 21300-series (smallest first) | 2 of 12 |
| Bore above smallest 21300-series size | 5 mm |
Cross references & equivalents
| Equivalent model | Brand | Match level | Note |
|---|---|---|---|
| 21311 | ISO 15 | full Dimensions and internal design equivalent — standard interchange. | ISO 15 boundary-dimension envelope; brand-specific OEM equivalents (NSK/FAG/NTN) 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 21311 model number is decoded
In the 21300-series (ISO 15 dimension series) the leading 2 marks a double-row spherical roller and the last two digits of 21311 encode the bore: code 11 = 55 mm (code × 5 from 04 upward). The ISO 15 envelope is 120 mm outside diameter and 29 mm width — 2.165 × 4.724 × 1.142 in, with a 32.5 mm radial section height. Two rows of symmetrical barrel rollers on a common sphered outer raceway self-align to shaft deflection while carrying heavy radial load and bidirectional axial load. Typical catalogue practice for a rotating inner ring is a k5 shaft seat, H7 housing and C3 internal clearance; K variants use a 1:12 tapered bore on an adapter sleeve — verify against the mounting arrangement.
Typical equipment & failure modes
Common applications
- industrial gearbox and drive shafts
- elevator winches and hoist drums
- process crane travel wheels
- conveyor head and tail pulleys
- vibrating screens, feeders and shakeout machines
Known failure patterns
- roller smearing and skid marks when the radial load falls below the minimum load needed to drive the roller set
- cage fatigue and fracture on vibratory screens supplied with normal CN clearance instead of a vibratory C4 fit
- fretting corrosion on a tapered-bore sleeve seat when drive-up is insufficient and the inner ring works on the adapter
- lubricant starvation and cage wear where the relubrication interval ignores the slow-speed, dirty operating regime
- water and grit pitting of open bearings in mining and pulping duty after the housing seals degrade
Selection pitfalls — read before you substitute
- On this 55 mm-bore 21311, specify C3 clearance as the default for an interference inner-ring fit and verify residual play after mounting; a medium-section row that ran free on the bench can be fully clamped at operating temperature on the 55 mm shaft.
- The 213 series at 55 mm bore keeps the 29 mm width comparatively narrow for its 120 mm OD; it fits restricted axial space but carries less load than a 22311, so substitution into heavy 223 duty — even at identical bore and OD — will shorten life.
- Check the shoulder geometry for 21311: a generous fillet on the 55 mm shaft looks strong but stops the 29 mm inner ring seating home; use the catalogue corner-relief radius and provide a withdrawal groove so the 32.5 mm-section outer ring presses flush in the 120 mm housing.
- Large 21311 tapers should be mounted with a hydraulic nut or oil injection: controlled drive-up sets the residual radial clearance on the 29 mm-wide double row, whereas bar-and-spanner force either under-drives (fretting) or over-drives (thermal seizure on first hot run).
- Read the damage pattern on a removed 21311: spalling concentrated on one side of the 120 mm outer race points to misalignment or thrust overload, while uniform roller-end smearing means minimum-load skidding — the two failures demand opposite corrections.
- Press 21311 using the right ring: force on the inner ring for an interference shaft fit and on the outer ring for a housing fit — transmitting mounting force through the barrel rollers brinells the sphered raceways of the 120 mm assembly.
- Match the cage to the duty: the E/CC stamped window-steel cage is the standard for general 21311 service, while the machined brass CA cage is preferred for heavy shock and vibratory applications — never replace a CA row with a CC row in a screen or crusher without re-rating.
Frequently asked questions
What are the dimensions of a 21311 spherical roller bearing?
A 21311 double-row spherical roller bearing per ISO 15 has a 55 mm bore, 120 mm outer diameter and 29 mm width (2.165 × 4.724 × 1.142 in), a 32.5 mm radial section and roughly 1322 g geometry-based estimated mass; catalogue masses vary with cage and design.
How does the 21311 bore code work?
The leading 2 in 21311 denotes a double-row spherical roller, the middle digits give the ISO 15 dimension series, and the last two digits are bore code 11: 11 × 5 = 55 mm. The 120 mm OD and 29 mm width come from the dimension series (21300), not from the bore code alone.
How much misalignment can a 21311 accommodate?
Thanks to the sphered outer ring raceway, 21311 normally accommodates angular misalignment of around 1° under load (up to about 2° in favourable, lightly loaded conditions); the permissible value is smaller under full load and depends on clearance and cage design, so check the catalogue figure for the actual duty.
What is the difference between 21311 and 21311K?
The plain 21311 has a cylindrical bore for a straight shaft seat. The K suffix denotes a 1:12 tapered bore, normally mounted on an H3xx adapter sleeve over a commercial shaft (or directly on a tapered journal); the bearing is driven up the sleeve to a specified residual clearance and locked with a KM nut and tab washer.
Should the 21311 be ordered with CN, C3 or C4 clearance?
Use C3 as the usual default when the rotating inner ring has an interference fit, because the fit plus thermal expansion reduces residual play; choose C4 (often with a vibratory cage design) for screens and feeders; order CN mainly for loose fits on stationary shafts or split housings. A W33 outer-ring lubrication groove is a separate, commonly combined option.
Reviewed & verified by the MPN Base engineering desk against source catalog iso15-srb-geometry on 2026-09-24. Read our editorial & correction policy.