RHP7205ETSULP4Super Precision Angular Contact Ball Bearing, SINGLE Universally Ground, 25 x 52 x 15 mm, 25°, Phenolic Cage, P4 Light Preload

Product Description

What this part is

An RHP super-precision single-row angular contact ball bearing: 25 mm bore, 52 mm outside diameter, 15 mm wide, with a 25° contact angle, a phenolic cage and P4 precision. This is a machine-tool spindle bearing. Every element of the designation exists to serve stiffness, accuracy and speed rather than raw load capacity.

Decoding the designation — and what SU actually promises:
7205 — single-row angular contact ball bearing, 72 dimension series, bore code 05 (25 mm).E — 25° contact angle in the RHP/NSK scheme. (C denotes 15°. This is verified against RHP/NSK world part numbering, where 7211C-T-P4S-DUL is the 15° build and 7220E-T-P4S-SUL the 25°.)T — machined phenolic cage. Usually visible as a brown or bronze-coloured cage in the photographs.SU — Single, Universally ground.L — Light preload. (M = medium, H = heavy.)P4 — ABEC 7 precision class.
SU is the specification most often misread, and it is a dispute waiting to happen if it is not stated plainly. SU means this is ONE bearing. It is not half of a matched set that has been split; it is a single bearing that was designed and sold singly.

What “universally ground” adds is the useful part. The faces of a universally ground bearing are ground to a controlled offset, so that any two bearings of the same designation, taken from stock at random, will stack together and produce the specified preload — and will do so in any of the three arrangements: back-to-back (DB), face-to-face (DF) or in tandem (DT). You do not need a factory-matched pair with sequential serial numbers. You buy two SUL bearings and you get a DUL pair.

So: if your spindle needs a light-preload duplex pair, order two of these. If you need a triplet, order three. The DUL designation you may see on a drawing describes how two bearings behave together, not a single part number. One SUL bearing arriving where a buyer expected a pair is the most common source of disappointment on super-precision listings, which is why it is in the title and the first line of the summary.

Why 25° and not 15°

Contact angle is the central trade-off in a spindle bearing and this one has been chosen deliberately. A larger angle steers more of the load path into the axial direction, so a 25° bearing has substantially higher thrust capacity and higher axial stiffness than a 15° bearing of the same size. The cost is speed: a larger contact angle increases ball spin and gyroscopic effects, generating more heat, so the practical speed ceiling comes down.

Put concretely: 15° is the choice for a high-speed, lightly thrust-loaded spindle — a grinder, a high-rpm router. 25° is the choice where the cut generates real axial force and the spindle must not deflect — drilling, heavy milling, boring. Substituting one for the other because the base number matched will either lose you rpm or lose you rigidity. Neither failure announces itself; the machine simply stops holding tolerance or stops holding temperature.

The phenolic cage is a genuine selling feature

Phenolic (fabric-reinforced resin) cages are used in super-precision bearings for reasons that matter at speed. Phenolic is light, so cage inertia and centrifugal loading are low. It is self-lubricating — the resin releases a trace of lubricant into the ball pockets. It runs quietly, damps vibration, and is gentle on the balls at high speed in a way steel is not. It is also the reason these bearings are usually oil-mist or oil-jet lubricated rather than heavily greased.

The limitation to know: phenolic has a lower temperature ceiling than steel or brass and is attacked by some synthetic lubricants and by water. Do not steam-clean a phenolic-caged bearing and do not run it hot.

Published data and what we have left blank

Bore (d): 25 mmOutside diameter (D): 52 mmWidth (B): 15 mmContact angle: 25° (E)Precision class: P4 / ABEC 7Preload: light (L)Cage: machined phenolic (T)Arrangement: SU — single, universally ground; stacks as DB, DF or DT with any other bearing of the same designationNumber of rows: 1
We have not published dynamic and static load ratings or a limiting speed for this designation. We could not retrieve them from NSK or from a reliable mirror, and load ratings for super-precision angular contact bearings vary with contact angle and cage type within the same base number — so borrowing a figure from a 7205C or a 7205B build would produce a number that looks authoritative and is wrong on the axis that matters. NSK’s technical service holds the RHP legacy data and can supply it against the full designation. An honest gap is more useful to you here than a plausible fabrication.

Quantity and configuration

One bearing in stock, and one bearing is what is supplied. If your spindle position takes a duplex pair you need two, and because the bearing is universally ground you may pair this one with any other 7205ETSULP4 rather than hunting a serial-matched partner.

Fitting notes

Treat it as a precision component: clean bench, no impact, press only on the ring being fitted, and never allow mounting force to pass through the balls. Preload in a universally ground stack is established by the ground faces, so the shaft and housing shoulders must be square and the clamping arrangement must not distort the rings — an over-tightened locknut or a cocked spacer throws away the P4 accuracy you paid for. Match the lubrication method to the phenolic cage: oil mist or light oil, not a heavy grease pack.

Interchange guidance

Search forms include 7205ETSULP4, 7205-E-T-SUL-P4, 7205 E T SUL P4, 7205ETSUL, 7205ETSULP4Q, 7205E, 7205. RHP’s bearing line was absorbed by NSK, so RHP super-precision designations map onto NSK’s current numbering — the equivalent NSK form is 7205CTYNSULP4 for the 15° build and the corresponding 25° designation for this one. Related builds: 7205ETDULP4 (a factory-matched duplex light-preload pair), 7205ETSUMP4 (medium preload), 7205ETSUHP4 (heavy preload), 7205CTSULP4 (15°). Same-envelope super-precision equivalents from FAG (B7205-E-T-P4S), SKF (7205 CD/P4A) and NTN exist at 25 × 52 × 15 mm — but verify contact angle, preload class and cage material, because all three differ between brands under similar-looking suffixes.