NSKSuper Precision Angular Contact Ball Bearing Matched Pair (2 Pcs), 50 x 90 x 20 mm, 15 Degree Contact Angle, Light Preload, ABEC-7 P4Y, Phenolic Cage

Product Description

What this part is

A factory-matched pair of NSK super-precision angular contact ball bearings in the ISO 7210 envelope, each bearing 50 mm bore, 90 mm outside diameter, 20 mm wide. Both are ground to NSK’s P4Y tolerance class, carry a 15° contact angle and run an outer-ring-guided phenolic resin cage. That combination is machine tool spindle territory: grinding heads, milling and turning spindles, high-speed rotary tables and precision boring heads.

Designation breakdown

Read against NSK’s own numbering system for high-precision angular contact ball bearings. Suffix letters are brand-specific, and the same characters mean different things in the SKF, FAG and Timken schemes.

7210: single-row angular contact ball bearing, 02 dimension series, bore number 10 = 50 mm bore, 90 mm outside diameter, 20 mm width. C: 15° contact angle. NSK’s standard series offers three angles, C = 15°, A5 = 25°, A = 30°. SKF’s AC = 25°, so a similar-looking suffix on an SKF number is a different bearing. TR: outer-ring-guided phenolic resin cage, rated by NSK to a 120°C operating limit and the high-speed cage choice for this family. DUL: DU universal arrangement (double row), L light preload. Universal grinding is what lets two bearings be stacked back-to-back, face-to-face or in tandem and arrive at a defined preload with no shims or spacers. P4Y: NSK special accuracy class, with bore diameter and outside diameter tolerances exclusive to NSK and tighter than standard, everything else to ISO Class 4 (ABEC 7).

The cartons also carry NSKHPS, NSK’s High Performance Standard branding, and each is stamped with its own serial (LA204878A and LA204878B) plus a ring-measurement grid, the deviation figures NSK records so the two rings match as a set.

Specifications in practice

A 15° contact angle sits at the high-speed, low-thrust end of the angular contact range. It buys radial rigidity and speed ceiling, and trades away axial load capacity and axial stiffness. For a spindle seeing heavy one-directional thrust, such as hard turning or heavy drilling, a 25° or 30° bearing is the corresponding part.

Light preload is the same trade in a different variable. Preload removes internal play so the shaft holds position under reversing load, and it also generates heat. NSK’s published light-preload figure for this bearing is 248 N, giving roughly 69 N per micrometre of axial rigidity. Medium preload raises that to about 102 N/µm at the cost of thermal headroom. Preload grades within one spindle stack are uniform, since a tighter bearing in a mixed stack carries load it was not sized for.

The phenolic cage is a high-speed feature. It is light, so cage inertia at speed is low, it is guided on the outer ring for stability at high dmn, and it holds oil in its pores, which helps under marginal lubrication. It also sets the temperature limit of the assembly, below that of a machined brass cage.

Published ratings and mounting data

Bore (d): 50 mm. Outside diameter (D): 90 mm. Width (B): 20 mm per bearing, 40 mm for the pair mounted. Contact angle: 15°. Basic dynamic load rating (Cr): 54,000 N per bearing. Basic static load rating (C0r): 31,500 N per bearing. Permissible axial load (Pa): 21.1 kN. Limiting speed: 16,500 rpm grease-lubricated, 25,000 rpm oil or oil-air. Effective load centre (a): 19.4 mm. Shaft abutment diameter (da min.): 57 mm. Housing abutment diameter (Da max.): 83 mm; Db max. 85 mm. Fillet radii: r min. 1.1 mm, r1 min. 0.6 mm; ra max. 1 mm, rb max. 0.6 mm. Light preload: 248 N; axial rigidity approximately 69 N/µm. Recommended grease quantity: 2.8 g per bearing. Tolerance class: P4Y (ISO Class 4 / ABEC 7, with NSK-exclusive bore and outside diameter tolerances). Cage: phenolic resin, outer-ring guided. Closure: open, no seals and no shields. Rows: one per bearing. Mass: approximately 0.457 kg per bearing, approximately 0.914 kg for the pair.

Speed figures are catalogue limiting speeds for the bearing alone. Achievable spindle speed follows preload, lubrication method, housing fit and cooling.

Set composition

This listing supplies two bearings, one matched DUL pair. Both cartons are sealed and shrink-wrapped together, serialised LA204878A and LA204878B, marked Made in England. DUL describes how two universally ground bearings behave when mounted together. This set is unsplit.

Because they are universally ground, the pair mounts back-to-back (DB) for moment stiffness and two-direction thrust, face-to-face (DF), or in tandem (DT) to double one-direction thrust capacity. No shims or ground spacers are needed to reach the specified light preload.

Mounting data

Angular contact bearings are directional. The outer ring has a thick land on one face and a thin land on the other, and the bearing takes thrust one way only. Both rings carry face markings. The two rings were measured and matched as a set. Shaft abutment diameter da min. is 57 mm, housing abutment Da max. 83 mm and Db max. 85 mm, with fillet radii ra max. 1 mm and rb max. 0.6 mm. An ABEC-7 bearing delivers the runout of the housing it sits in.

Interchange guidance

Cross-references for this 50 x 90 x 20 mm super-precision pair: SKF 7210 CD/P4ADGA (extra light preload), FAG B7210-C-T-P4S-UL (light preload), Timken/Fafnir 2MM9210WI DUL (15° contact angle), NTN 7210CT1GD2GL (universally ground duplex, light preload) and Barden 210HDL. Contact angle, tolerance class and preload grade each govern how the spindle behaves.

RHP super-precision spindle bearings were absorbed into NSK, so an RHP number in an old machine manual may legitimately point here.