NSK7928CTYNSULP4Super Precision Angular Contact Spindle Bearing 140 x 190 x 24 mm 15 Degree Contact Angle ABEC 7 P4 Light Preload Universally Ground Single

Product Description

What this part is

An NSK super-precision single-row angular contact ball bearing, 140 mm bore × 190 mm outside diameter × 24 mm width. This is a thin-section, large-bore spindle bearing — the 79-series envelope exists to put a very high running accuracy bearing into a shallow radial space, which is why you find it in machine-tool spindle noses, rotary tables, indexing heads, precision boring and grinding spindles, and large-diameter measuring and positioning axes. It is universally ground and set for light preload, so it is designed to be stacked with identical bearings to build the stiffness and thrust capacity a spindle needs.

Decoding the designation

7928 — 79-series single-row angular contact ball bearing, 140 mm bore. The ISO base designation for this bearing is 71928, which is why you will see it catalogued both ways.
C — 15° contact angle in NSK’s scheme. Be careful with this letter across brands: NSK uses C for 15°, A5 for 25° and A for 30°, whereas SKF’s AC is 25°. The same-looking suffix means a different angle depending on whose bearing you are holding, and the angle changes the stiffness and speed behaviour completely.
TYN — NSK’s moulded polyamide (nylon) cage, ball-centred.
SU — single, universally ground. This is the part that decides how many bearings you receive. See the quantity section.
L — light preload. The letter after SU or DU is the preload class: L light, M medium, H heavy.
P4 — ISO tolerance class 4, equivalent to ABEC 7.

What a 15° contact angle trades away

A 15° bearing carries its load closer to the radial plane than a 25° or 30° bearing. That gives higher radial capability and, more importantly, a higher speed ceiling: the shallower angle means less centrifugal and gyroscopic loading on the balls, less heat, and less spin at the contact. What you give up is thrust capacity and axial stiffness — the spindle will deflect more axially under the same cutting thrust than a 25° bearing would. That is the correct trade for high-speed, lighter-cut work such as grinding and high-rpm milling, and the wrong trade for a heavy boring or facing spindle. If your application is thrust-dominated, you want a steeper angle, not this bearing.

Why light preload matters more here than the precision class:
Everyone reads the P4 and stops. On a spindle bearing the preload class is the more consequential number. Light preload (L) generates less internal friction, so the bearing runs cooler, tolerates higher speed and is more forgiving of thermal growth in the shaft and housing. It also produces the least stiffness of the three classes, so the spindle deflects more under load. Heavy preload does the reverse: stiffer, hotter, slower. Crucially, preload classes cannot be mixed inside one stack — put an L next to an M and clamping brings the pair to a preload neither was designed for, unloading one bearing and overloading the other. The failure shows up as heat and short life, not as an obvious assembly error. Match the class across the whole set.

What universal grinding lets you do

Universally ground (the U in SUL) means the ring faces are ground to a controlled offset so that any two or more bearings of this designation will come up to the intended preload when clamped together in any orientation — no shims, no measuring, no factory-matched set paperwork. You can build a back-to-back (DB) pair for maximum moment stiffness and bidirectional thrust, a face-to-face (DF) pair where misalignment tolerance matters, a tandem (DT) stack to multiply thrust in one direction, or triplex and quadruplex arrangements. That interchangeability is the reason to buy universally ground stock rather than a sealed matched set.

Published ratings and mounting data

Confirmed geometry and designation data

Bore 140 mm
Outside diameter 190 mm
Width 24 mm
Contact angle 15°
Precision class ISO P4 (ABEC 7)
Preload class: light
Cage: moulded polyamide (nylon), ball-centred
Rolling elements: steel balls
Closure: open, no seals or shields
Grinding: universal, single (SU)

Basic dynamic and static load ratings, limiting speed and preload force are deliberately left blank. NSK’s own catalogue page for this designation was not reachable, and the load-rating figures circulating for it on aggregator sites trace back to secondary listings rather than to NSK. Load ratings on super-precision bearings vary with cage, preload and grinding class, and a borrowed number on a spindle rebuild is worse than no number. Ask us and we will chase the figures with NSK, or take them from your own NSK catalogue against the exact designation.

Quantity and configuration

This listing ships one bearing. The SU in SUL means single universally ground — as distinct from DU, duplex, which describes how two bearings behave together. A single universally ground bearing is a building block: it is intended to be combined with other bearings of the same designation and preload class, and it is complete and correct on its own. If you need a matched pair, a triplex or a quadruplex set, you need the corresponding number of pieces — contact us for availability before ordering rather than assuming a pair is on its way.

Correcting the source data

The previous description quoted a dynamic load rating of 66 kN and a static load rating of 83 kN. We have removed both. Those figures could not be traced to NSK and appear to originate in secondary marketplace listings for this same item, which makes them circular rather than sourced. The previous copy also framed the bearing as a general “industrial automation and motion control” component and said nothing about preload class, cage material, universal grinding or how many bearings ship — the facts a spindle buyer actually needs. Those are now stated.

Fitting notes

Super-precision bearings punish careless handling. Keep the bearing in its wrapper until the moment of assembly, work clean, and never wash out the preservative with a solvent that leaves residue. Press only on the ring that takes the interference fit and never drive assembly load through the balls. Shaft and housing seats must be ground to a tolerance and roundness consistent with a P4 bearing — fitting an ABEC 7 bearing into a sloppy or out-of-round housing throws away the accuracy you paid for, and is the single most common reason a rebuilt spindle does not hold size. Clamp uniformly through a properly faced locknut or spacer so preload comes up evenly around the ring, check that shoulder and fillet dimensions clear the bearing corners, and lubricate to your spindle’s specification before running. On a thin-section 79-series bearing, housing distortion and shoulder squareness matter more than they do on a heavier section.

Interchange guidance

The same bearing is catalogued as 7928C, 7928CTYNSULP4, 7928-C-TYN-SUL-P4 and under the ISO base number 71928 / 71928-C. Same-envelope 140 x 190 x 24 mm, 15°, P4 universally ground singles are made by Schaeffler/FAG (B71928-C-T-P4S-UL), SKF (71928 CD/P4A) and NTN (7928C). If you are working from old RHP paperwork, note that RHP precision bearings were absorbed into NSK — the current designation for an RHP-era spindle bearing is an NSK one, which is why an RHP part number search returns nothing in a live catalogue. Whichever brand you substitute, match the contact angle, the preload class and the tolerance class, and do not mix cage types within one preloaded stack.