71811 bearing: complete specifications & equivalents
The 71811 is a ISO 15 radial bearing sized 55 x 72 x 9 mm (bore x OD x width). Verify dimensions against the official catalog before ordering.
Specification table
| Parameter | Value |
|---|---|
| Brand | Generic ISO interchange (unbranded) |
| Bore diameter d | 55 mm |
| Outer diameter D | 72 mm |
| Width B | 9 mm |
| Seal / shield | open |
| Internal clearance | CN / C3 available |
| Tolerance class | P0 |
| Cage | brass |
| Operating temperature | -40 to +150 °C |
| Mass (geometry estimate) | 78 g |
| Standard | ISO 15 |
| Catalog version | iso15-ed4-geometry |
| Last verified | 2026-09-24 |
Source: ISO 15 boundary-dimensions standard · extracted 2026-09-24
Standard-interchange bearing: dimensions per ISO 15; CN clearance, P0 tolerance and a stamped-steel cage are catalogue defaults unless the supplier states otherwise, and mass is a geometry-derived estimate. Brand catalogue load ratings and limiting speeds for 71811 are being backfilled — use the inquiry form for certified values.
Dimensions in inches & 71800-series range
| Bore d | 2.165 in |
|---|---|
| Outer diameter D | 2.835 in |
| Width B | 0.354 in |
| ISO bore code | 11 |
| Radial section height (D−d)/2 | 8.5 mm |
| Smallest bore in 71800-series | 20 mm |
| Largest outer diameter in 71800-series | 125 mm |
| Width range across 71800-series | 7–13 mm |
| Bore position in 71800-series (smallest first) | 8 of 17 |
| Bore above smallest 71800-series size | 35 mm |
Cross references & equivalents
No verified interchange data yet. Send an inquiry and our team will confirm equivalents manually.
How the 71811 model number is decoded
In the 71800-series (ISO 15 diameter series 8) the last two digits encode the bore: 71811 carries bore code 11 = 55 mm. Outside diameter 72 mm and width 9 mm come from the ISO 15 boundary-dimensions general plan, shared with the 61811 deep-groove envelope. The '7' prefix marks a single-row angular-contact design with an asymmetric raceway and a nominal 40° contact angle (suffix C); a higher-angle variant carries more axial load, a 25° (E / A5) variant runs faster. For combined radial and axial load with a rotating inner ring on a 55 mm shaft, specify a k5 shaft seat with an H7 housing bore — verify against the load direction and magnitude, and pair two units (DB or DF) for bidirectional thrust.
Typical equipment & failure modes
Common applications
- precision rotary tables
- medical and lab spindles
- clutch and idler shafts
- semiconductor handling axes
Known failure patterns
- electric pitting in VFD-driven spindles without shaft grounding protection
- raceway spalling from axial overload exceeding the single-direction thrust rating
- preload loss after a paired set runs loose, letting the balls skid and smear the raceway
- raceway smearing under marginal lubrication at start-up before oil climb reaches the contact
Selection pitfalls — read before you substitute
- Thermal expansion on this 55 mm bore consumes preload in a DB pair; size the preload class and clearance for the operating temperature, not the cold state.
- The 718xx thin section at 55 mm bore has only a 8.5 mm radial section height: it saves space but is highly sensitive to misalignment and deflection — verify spindle stiffness before choosing it over a 7211.
- Pair thin-section 71811 units as a factory-matched set (universal SU/DU pairing): bench-pairing two singles with only 8.5 mm of section gives uncontrolled preload — order DB or DF pairs as one line item for the 55 mm spindle seat.
- Assign fits by which ring rotates: an interference shaft fit for a rotating inner ring; if the outer ring rotates instead, reverse the logic — a loose rotating ring creeps and frets its seat.
- A single 71811 angular-contact bearing takes axial load in ONE direction only — for bidirectional thrust, mount a matched pair (DB back-to-back or DF face-to-face), never rely on one row.
Frequently asked questions
What are the dimensions of a 71811 angular-contact bearing?
A 71811 single-row angular-contact ball bearing has a 55 mm bore, 72 mm outer diameter and 9 mm width (2.165 × 2.835 × 0.354 in), per ISO 15 boundary dimensions. It is an open bearing with a nominal 40° contact angle. Geometry-based estimated mass is about 78 g for a brass-cage unit; catalogue masses vary with cage and ball complement.
How does the 71811 bore code work?
The last two digits of 71811 are bore code 11, giving 11 × 5 = 55 mm bore. The 72 mm outside diameter and 9 mm width follow the ISO 15 diameter series, shared with the 61811 deep-groove envelope.
What is the contact angle of 71811?
The nominal contact angle is 40° (suffix C): a higher angle carries more axial load but limits speed. A 25° (suffix E or A5) variant runs faster and is preferred for high-speed spindles; a 15° (suffix C7) version exists for very-high-speed duty. Confirm the angle and ball complement in the supplier catalogue.
Can a single 71811 take axial load in both directions?
No. A single-row angular-contact bearing carries axial load in one direction only. For bidirectional thrust, mount a matched pair — DB (back-to-back) for a rigid, moment-resisting arrangement with preload class light (L) for speed or heavy (H) for stiffness, DF (face-to-face) for thermal expansion tolerance, or DT (tandem) to share one-direction load.
How fast can a 71811 run?
Thin-section angular-contact bearings reach high speeds because the 8.5 mm section keeps the ball set light, but the practical limit is set by the lubricant and the precision of the 55 mm seat rather than the geometry alone; a 25° (E/A5) contact-angle variant and a light (L) preload class run faster than a 40° heavy-preloaded pair. Confirm the limiting speed in the supplier catalogue.
Reviewed & verified by the MPN Base engineering desk against source catalog iso15-ed4-geometry on 2026-09-24. Read our editorial & correction policy.