RHP7217CTSULP4Super Precision Angular Contact Ball Bearing 85x150x28 mm, 15° Contact Angle, Phenolic Cage, ABEC 7, Light Preload, Single Universally Ground, Medium 72-Series Section

Product Description

What this part is

A single-row super precision angular contact ball bearing in the ISO 72-series medium section — 85 mm bore, 150 mm outside diameter, 28 mm width. It is a machine tool spindle bearing with a 15° contact angle, a machined phenolic cage, ABEC 7 running accuracy, and faces universally ground for light preload.

Decoding the designation

72 – ISO 72-series medium section angular contact ball bearing
17 – bore code, 85 mm bore
C – 15° nominal contact angle
T – machined phenolic cage
SUL – single, universally ground, light preload
P4 – ISO tolerance class 4, equivalent to ABEC 7

The alternative numbers on this item corroborate that decode rather than contradict it. The Timken/Fafnir world number 2MM217WI CR SUL reads the same way in a different scheme: 2MM denotes a 15° contact angle, CR a phenolic outer-land-riding cage, SUL single universally ground light preload. 217HDL is a legacy RHP-era designation for the same bearing, and B7217CTPAP4UL is an alternative super precision form carried on the source data.

Correcting the source data

The previous copy stated the bearing was manufactured in the United Kingdom. No carton or ring marking has been verified to support that, and origin markings on surplus super precision bearings are frequently not what the listing says, so no origin is claimed here. Copy describing this bearing as suited to “commercial” general use or to “equipment enthusiasts” has also been removed — a P4 spindle bearing needs fitted-tolerance seats and controlled lubrication, and selling it into general-purpose use produces returns, not satisfied buyers.

What these specs mean in practice

The 15° contact angle is the speed-and-radial-stiffness choice. Because the ball contact line lies closer to the radial plane, less of the load is turned into thrust, which keeps ball centrifugal and gyroscopic effects and cage loading low. The result is a bearing that runs faster and cooler than a 25° or 30° bearing of the same size, with more radial stiffness. What you trade away is axial capacity and axial stiffness. If your spindle takes heavy one-directional thrust, the 25° E variant in the same envelope is the better tool.

Light preload follows the same reasoning. Preload eliminates the internal looseness that would let balls skid instead of roll, and it makes stiffness predictable — but it also generates friction heat, and heat in a spindle bearing changes the preload it was set to. The light grade gives the highest permissible speed and the lowest temperature rise of the three, at some cost in stiffness under cutting load. It is the right pick for a high-rpm finishing or grinding spindle; heavy roughing usually wants medium.

The 72-series medium section gives this bearing more material and larger balls than a 70-series bearing on the same 85 mm shaft, so it carries more load — useful because the light preload is giving stiffness away elsewhere.

The phenolic cage is light, damps well and retains lubricant in its own porosity, which is why phenolic-caged bearings survive marginal lubrication far better than steel or brass. Phenolic sets a maximum operating temperature, so it does not belong in a hot, uncooled housing.

Quantity and configuration

The SU in the designation means single universally ground: this is one bearing. Universal grinding means it can run alone or be combined with another bearing of the identical designation to form a back-to-back, face-to-face or tandem set that reaches the specified light preload with no shims and no grinding. If you need a pair, order two of the same designation.

Fitting notes

A universally ground bearing has a defined high face and low face. Used singly this affects which way round it goes; used in a set the ring markings determine the arrangement, and getting it wrong throws away the preload the grind was there to create. Choose the arrangement deliberately — back-to-back for stiffness and moment capacity, face-to-face where shaft-to-housing alignment cannot be held tightly, tandem to share thrust in one direction between two bearings.

Precision practice throughout: clean, round, burr-free shaft and housing seats to the tolerances the P4 class assumes; even, symmetrical clamping so the outer ring is not pinched out of round; a controlled fill of clean lubricant, since over-greasing a light-preload spindle bearing is one of the quickest routes to a high running temperature and a lost preload. Never hammer, and never pass mounting load through the balls.

Published ratings and mounting data

Basic dynamic load rating, basic static load rating and limiting speed are left blank. NSK’s super precision bearing tables were not retrievable at the time of writing, and figures published for other contact-angle variants in the same 85x150x28 envelope are not this bearing’s figures. An honest gap is more useful to a specifying engineer than a borrowed number; take the values from the current NSK super precision catalogue.

Interchange guidance

RHP is now NSK, and NSK carries the super precision line forward, so this cross-shops against NSK 7217CTRSULP4 and 7217CTYNSULP4. Timken/Fafnir equivalent: 2MM217WI CR SUL — note that Fafnir MM-prefixed numbers normally carry P4S, a tighter class than P4. Same-envelope equivalents elsewhere: SKF 7217CD/P4A, FAG B7217C.T.P4S, NTN 7217C in its universally ground light-preload form. Match envelope, contact angle, tolerance class and preload grade before substituting, and do not treat a 15° C bearing as a drop-in for a 25° or 30° one.