SKF21308Double-Row Spherical Roller Bearing 40 x 90 x 23 mm, Narrow 213 Series, Straight Bore, Lubrication Groove and Holes, 1 Pc

Product Description

What this part is

An SKF double-row spherical roller bearing, 40 mm bore, 90 mm outside diameter, 23 mm width, in the ISO 213 dimension series. Two rows of barrel rollers share one spherical outer raceway, so the inner ring and roller set swivel bodily inside the outer ring. That self-aligning action absorbs shaft deflection and housing misalignment that would destroy a cylindrical roller or deep groove ball bearing of the same size, while carrying heavy radial load and thrust in both directions.

Decoding the designation

213 is the double-row spherical roller bearing in dimension series 13, the narrow section of the spherical roller family: at 40 x 90 mm it is 23 mm wide, where the wider 222-series 22308 in the same bore and outside diameter is 33 mm. The narrow section is what fits a width-constrained housing. 08 is the bore code for a 40 mm bore. There is no K, so the bore is straight and cylindrical. There is no clearance suffix, so the bearing carries normal, CN, radial internal clearance.

Lubrication feature and the SKF W convention

On SKF’s 213, 222 and 223 series the current E design carries the annular lubrication groove and three lubrication holes in the outer ring as standard, with no suffix at all, so the absence of a W33 in this designation does not mean the feature is missing. SKF W on its own carries the opposite sense: a bearing marked W is one without the groove and holes. The lubrication groove lets grease or oil be fed straight into the roller rows through the housing rather than relying on lubricant migrating in from the ends, and relubrication is the largest single factor in spherical roller bearing life. The feature needs a housing whose lubrication port lines up with the groove; in a plain bore it goes unused.

What these specs mean in practice

The straight bore mounts directly onto a plain 40 mm shaft seat. It is a shaft-seat mounting rather than a sleeve mounting, which is the practical difference between it and a 21308 K. Normal clearance suits a moderate shaft interference fit in a housing that does not run hot; where the shaft fit is heavy or the machine runs warm, the C3 version is the corresponding choice, because the inner ring grows on the shaft and under heat and takes up the clearance it started with.

Published ratings and mounting data

SKF publishes the following for the 21308 E in current Explorer production. Basic dynamic load rating C: 107 kN (24,040 lbf). Basic static load rating C0: 108 kN (24,270 lbf). Fatigue load limit Pu: 11.8 kN. Reference speed 7,000 rpm and limiting speed 9,500 rpm. Mass approximately 0.75 kg.

Quantity and configuration

1 Pc. One complete bearing: inner ring with both roller rows and cage, plus the outer ring. Spherical roller bearings are a non-separable assembly, so there is no cup, cone or separate ring. The bore is straight, so no adapter sleeve, locknut or lockwasher applies. No housing supplied.

Fitting notes

Mounting force is applied to the inner ring and not through the rollers. A bearing this size takes a genuine interference fit, so it is heated to roughly 80 to 100 °C above the shaft in an induction heater or a clean oil bath rather than pressed on cold. The outer ring is seated squarely in the housing bore and left to take up its own alignment before the assembly is drawn down, since clamping the outer ring off-neutral during build removes the self-aligning capability. The housing lubrication port is aligned with the outer-ring groove and the groove purged with grease before the first run.

Interchange guidance

The current SKF designation for this bearing is 21308 E. SKF catalogues the older CC design only up to 21307, so from 21308 upward the E design took over and a 21308 CC on a carton is a legacy number whose current-production replacement is 21308 E. Other dimensionally equivalent straight-bore 21308 bearings include FAG 21308-E1-XL, NSK 21308EAE4, NTN 21308EAW33 and NTN-SNR 21308EAW33. The lubrication codes are one feature under different letters: standard and unmarked on SKF E and FAG E1, W33 where a maker marks it explicitly, E4 on NSK, S on FAG’s older codes, D1 on NTN Japan, B33 on legacy SNR. Any 21308 K or EK is the tapered-bore version, requiring an H308 adapter sleeve: same envelope, different mounting, and a related size rather than a substitute. The wider-section 22308 shares the 40 x 90 mm bore and outside diameter but is 33 mm wide, so it is a related size too.