21318 bearing: complete specifications & equivalents
The 21318 is a ISO 15 radial bearing sized 90 x 190 x 43 mm (bore x OD x width). Verify dimensions against the official catalog before ordering.
Specification table
| Parameter | Value |
|---|---|
| Bore diameter d | 90 mm |
| Outer diameter D | 190 mm |
| Width B | 43 mm |
| Seal / shield | open |
| Internal clearance | CN / C3 / C4 available |
| Tolerance class | P0 |
| Cage | steel |
| Operating temperature | -30 to +120 °C |
| Mass (geometry estimate) | 4825 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 21318 are being backfilled — use the inquiry form for certified values.
Dimensions in inches & 21300-series range
| Bore d | 3.543 in |
|---|---|
| Outer diameter D | 7.48 in |
| Width B | 1.693 in |
| ISO bore code | 18 |
| Radial section height (D−d)/2 | 50 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) | 9 of 12 |
| Bore above smallest 21300-series size | 40 mm |
Cross references & equivalents
| Equivalent model | Brand | Match level | Note |
|---|---|---|---|
| 21318 | 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 21318 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 21318 encode the bore: code 18 = 90 mm (code × 5 from 04 upward). The ISO 15 envelope is 190 mm outside diameter and 43 mm width — 3.543 × 7.48 × 1.693 in, with a 50.0 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
- heavy conveyor drum pulleys
- cement and aggregate processing machinery
- mining and aggregate vibrating screens
- jaw and cone crusher eccentric shafts
- paper machine drying cylinders
Known failure patterns
- raceway and roller spalling after the L10 life or from sustained overload and shock in crusher duty
- 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
Selection pitfalls — read before you substitute
- The large 90 mm-bore 21318 mounts with real force: use induction heating or hydraulic drive-up on the tapered seat, measure residual clearance in micrometres, and plan lifting fixtures — the 43 mm double-row assembly cannot be drifted into position without brinelling.
- The 213 series at 90 mm bore keeps the 43 mm width comparatively narrow for its 190 mm OD; it fits restricted axial space but carries less load than a 22318, so substitution into heavy 223 duty — even at identical bore and OD — will shorten life.
- The 43 mm-wide 21318 seats against shaft and housing shoulders whose fillet must clear the bearing chamfer: keep the corner radius small enough that the 90 mm bore and 190 mm OD faces abut square — an undercut beats an oversized radius, which lifts the ring and edge-loads the 50.0 mm section.
- For a cylindrical-bore 21318, warm the inner ring to 80–100 °C (induction heater, never a flame) and slide it dry to the shoulder of the 90 mm shaft; cooling creates the interference, while hammering cold through the 190 mm assembly dents the sphered raceways.
- When reusing a sleeve-mounted 21318, inspect the adapter and lock parts together with the bearing: a stretched sleeve or a bent lockwasher tab that let the inner ring creep on the 90 mm journal must be replaced, or the new bearing frets the same seat.
- Specify W33 when the 43 mm-wide bearing must be relubricated in place: it is the outer-ring annular groove with lubrication holes; without W33 grease only reaches the contacts through the shaft or housing arrangement.
- Press 21318 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 190 mm assembly.
Frequently asked questions
What are the dimensions of a 21318 spherical roller bearing?
A 21318 double-row spherical roller bearing per ISO 15 has a 90 mm bore, 190 mm outer diameter and 43 mm width (3.543 × 7.48 × 1.693 in), a 50.0 mm radial section and roughly 4825 g geometry-based estimated mass; catalogue masses vary with cage and design.
How does the 21318 bore code work?
The leading 2 in 21318 denotes a double-row spherical roller, the middle digits give the ISO 15 dimension series, and the last two digits are bore code 18: 18 × 5 = 90 mm. The 190 mm OD and 43 mm width come from the dimension series (21300), not from the bore code alone.
How much misalignment can a 21318 accommodate?
Thanks to the sphered outer ring raceway, 21318 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 21318 and 21318K?
The plain 21318 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 21318 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.