NSKNNU4928MBDouble Row Cylindrical Roller Bearing Outer Ring Assembly 140x190x50 mm, Brass Cage, Straight Bore, No Inner Ring

Product Description

What this part is

A double-row cylindrical roller bearing in the 140 mm bore × 190 mm outside diameter × 50 mm width envelope. Outer ring, two rows of rollers and a machined brass cage, with a straight bore.

Product scope

Outer ring, roller and cage assembly only. No inner ring. The matching inner ring is the plain sleeve for an NNU4928.

Decoding the designation

The NNU prefix marks a double-row cylindrical roller bearing in which the outer ring carries the guiding ribs and both roller rows, and the inner ring is a plain ribless sleeve. That is the reverse of the NN design, where the ribs sit on the inner ring. The 49 gives the dimension series and the bore code 28 gives a 140 mm bore, since ISO bore codes above 04 are multiplied by five. MB is the machined solid brass cage. There is no K suffix, so the bore is straight rather than a 1:12 taper.

What these specs mean in practice

Two rows of cylindrical rollers give very high radial capacity and high radial stiffness in a short axial length, which is why the NNU and NN types are the standard non-locating radial bearings in machine-tool spindles and heavy gearboxes. Line contact between roller and raceway spreads load over a length rather than a point, so radial capacity is far above a ball bearing of the same envelope. The design carries no axial load and provides no axial location; a separate thrust or angular contact bearing sets the shaft position. The machined brass cage tolerates higher temperature and more marginal lubrication than a pressed-steel cage and suits high speed and heavy load together.

Separable construction

Because the inner ring is a plain sleeve with no ribs, it separates completely from the outer ring assembly. That is what makes the two halves independently mountable: the sleeve goes onto the shaft and the outer assembly into the housing, and the two are brought together on assembly.

Quantity and configuration

1 Pc. One outer ring assembly, supplied without the inner ring sleeve, without a housing and without a locknut.

Fitting notes

The outer assembly seats in a ground housing bore against a square shoulder. With the inner ring absent the two halves are mated on assembly, and the roller set is aligned to the sleeve as the shaft enters. Cylindrical roller bearings of this class are sensitive to housing roundness, since an out-of-round bore concentrates load on part of the roller length.

Interchange guidance

The same-spec equivalents are SKF NNU4928B/SPW33 in its brass-cage form, FAG NNU4928-S-M-SP and NTN NNU4928. A tapered-bore NNU4928K is a related size rather than a substitution, since it mounts on a tapered journal instead of a cylindrical one. An NN4928, with the ribs on the inner ring, is a different design in the same envelope.