RU42 Cross Roller Bearing | 20×70×12 mm

RU42 Cross Roller Bearing Overview

The RU42 cross roller bearing is an ultra-compact, mounting-holed bearing for precision mechanisms where installation diameter, axial width and total rotating mass must remain low. Its main dimensions are 20 mm bore, 70 mm outside diameter and 12 mm width. As one of the smallest standard models in the RU series crossed roller bearings, RU42 uses integrated inner and outer rings with mounting holes on both rings. This structure allows direct installation onto accurately machined supporting components. Cylindrical rollers are arranged alternately at 90 degrees. The RU42 cross roller bearing can therefore support radial loads, axial loads in both directions and overturning moments within one compact unit.

Key RU42 Advantages

• Compact 70 mm outside diameter
• Thin 12 mm axial width
• Low approximate mass of 0.29 kg
• Integrated inner and outer rings
• Direct mounting holes on both rings
• Supports combined radial, axial and moment loads
• Suitable for inner- or outer-ring rotation
• Open, sealed and low-torque options

RU42 Cross Roller Bearing Specifications

The stated RU42 cross roller bearing load ratings are radial catalog values. They should not be treated as the allowable radial, axial or moment load of the complete mechanism without an application-specific calculation. Actual bearing life depends on the combined load, moment arm, speed, operating cycle, lubrication, preload, contamination and mounting accuracy.

RU42 Cross Roller Bearing Design Characteristics

Ultra-Compact Mounting Envelope

RU42 provides combined-load capability within a 70 mm outside diameter and 12 mm width. It is particularly useful where a conventional paired-bearing arrangement would occupy too much axial space. Its low mass also helps reduce the rotating inertia of lightweight joints, optical platforms and small positioning axes.

Integrated Inner and Outer Rings

Both rings are manufactured as integrated components. Compared with crossed roller bearings using a split ring, this construction reduces sensitivity to ring separation and simplifies handling during installation.

Direct Mounting Holes

The inner ring contains six M3 threaded holes on a 28 mm PCD. The outer ring contains six Ø3.4 mm through holes with Ø6.5 mm counterbores on a 57 mm PCD. These holes allow compact face mounting, but the supporting surfaces must still provide adequate flatness, rigidity and contact area.

20 mm Center Passage

The bore can accommodate a small shaft, cable bundle, air line or sensor wiring. The full nominal 20 mm diameter should not normally be treated as usable cable space; clearance is required for movement, protective sleeves and manufacturing tolerances. View the complete cross roller bearing range when a different bore size, ring structure or mounting method is required.

RU42 Cross Roller Bearing Variants

A typical purchasing specification may be written as: RU42UU / P4 / CC0 / low-torque grease Suffix conventions vary between manufacturers. The approved LYDL drawing and purchase order should therefore define the accuracy, clearance or preload, seals, lubricant and acceptable rotational torque.

Open RU42 or Sealed RU42UU?

Open RU42 is normally preferred for clean equipment, external sealing arrangements or applications requiring minimum seal resistance. RU42UU includes seals on both sides. It offers improved grease retention and contamination protection but may produce higher starting torque. Because RU42 is often driven by a small servo motor, the proportional effect of seal drag, grease consistency and preload can be more noticeable than on a larger RU bearing. Torque-sensitive projects should specify an acceptable starting and running torque range.

RU42 Cross Roller Bearing Applications

Small Robot Joints and End-Effectors

The 70 mm outside diameter and 12 mm width help reduce joint size. RU42 can be used in small robot wrists, gripper rotation axes and compact end-effectors.

Camera, Optical and Sensor Platforms

The bearing can support cantilevered cameras, lenses or sensors where overturning rigidity and repeatable angular positioning are required.

Compact Rotary Actuators

RU42 is suitable for servo-driven actuators, small indexing units and direct-mount rotary modules where component count and axial length must be controlled.

Inspection and Laboratory Equipment

Typical uses include sample rotation, optical inspection stages, measuring instruments and laboratory automation operating at controlled speed.

Selecting RU42, RU66 or RU85

• Choose RU42 when minimum size, low mass and a 20 mm passage are the main priorities.
• Choose the RU66 cross roller bearing when a 35 mm bore and substantially higher load ratings are required.
• Choose the RU85 cross roller bearing when the design needs a 55 mm passage, larger mounting interface or higher static-load capacity.

The comparison is intended for preliminary selection. The cross roller bearing selection guide provides more information about load directions, ring structures and application calculations.

RU42 Cross Roller Bearing Interchange Reference

The reference models share commonly used boundary dimensions and mounting patterns. However, load ratings, tolerances, seals, preload and rotational torque may differ between brands or product revisions. Before replacement, verify:

• 20 × 70 × 12 mm boundary dimensions
• 28 mm and 57 mm mounting PCDs
• M3 threads and counterbore depth
• Shoulder dimensions
• Seal arrangement
• Accuracy and runout tolerances
• Clearance or preload
• Starting and running torque
• Dynamic and static load ratings
• Lubricant and operating environment

THK and IKO are trademarks of their respective owners. They are referenced only for model identification and dimensional comparison. LYDL is an independent manufacturer and is not affiliated with or endorsed by these companies.

RU42 Cross Roller Bearing Installation

Small bearings are especially sensitive to burrs, particles and uneven mounting pressure. A small defect beneath the ring can represent a significant proportion of the required running accuracy.

1. Clean the bearing and both mounting faces.
2. Remove burrs from locating shoulders and bolt holes.
3. Verify the 28 mm and 57 mm mounting PCDs against the approved drawing.
4. Confirm that the M3 screws provide adequate engagement without bottoming out.
5. Place the bearing onto the mounting surface without hammering.
6. Install all fasteners loosely before final tightening.
7. Tighten the screws gradually in a diagonal sequence.
8. Rotate the bearing during staged tightening.
9. Measure axial and radial runout after installation.
10. Confirm starting torque before final servo adjustment.

Avoid using an excessive tightening torque on the M3 mounting points. The bolt grade, thread engagement, supporting material and lubrication condition should be considered when defining the final torque.

RU42 Cross Roller Bearing Inspection and Packaging

LYDL can inspect RU42 according to its accuracy, preload and documentation requirements.

Inspection Items

• Bore, outside diameter and width
• Mounting-hole diameter and PCD
• M3 thread inspection
• Ring roundness
• Raceway geometry and surface quality
• Material hardness
• Radial clearance or preload
• Starting and running torque
• Radial and axial runout
• Rotation smoothness and noise
• Appearance and marking

For P4, P2 or torque-controlled orders, the inspection requirements should be confirmed before production so that the relevant results can be included in the final report. After inspection, each bearing receives anti-rust protection and sealed or vacuum packaging. Shock-resistant material, individual cartons and reinforced export cases are available according to quantity and shipping method.

Why Source an RU42 Cross Roller Bearing From LYDL?

LYDL manufactures precision crossed roller bearings in Luoyang, China. Manufacturing and inspection capabilities cover ring machining, heat treatment, raceway grinding, superfinishing, component sorting, cleaning, assembly, preload control and final inspection. Available RU42 options include:

• Open or double-sealed construction
• P5, P4 and P2 accuracy
• Controlled clearance or preload
• Low-torque grease and seal selection
• Customer model and serial marking
• Dimensional, hardness and runout reports
• Material certificates and traceability
• OEM and export packaging

RU42 Cross Roller Bearing FAQ

Can RU42 replace a pair of miniature angular-contact bearings?

In some compact combined-load applications, one RU42 can replace a paired-bearing arrangement and reduce axial space. The replacement must still be checked for load capacity, rigidity, speed, torque and service life.

Can the RU42 cross roller bearing carry a cantilevered camera or tool?

RU42 can support overturning moment, but the moment must be calculated from the applied force and its distance from the bearing center. The mounting plate and bolts must also provide sufficient rigidity.

Why can a small mounting particle cause noticeable RU42 runout?

RU42 is only 12 mm wide and uses compact mounting interfaces. A burr or particle beneath either ring can tilt the bearing, change the preload distribution and increase installed runout.

Is the full 20 mm bore available for cable routing?

Not normally. Space should be reserved for cable movement, bend radius, protective sleeves, connectors and installation tolerances.

Will RU42UU increase the required servo torque?

Usually, the seals create additional resistance. Preload and grease also affect torque. A low-torque version should be specified when the available motor torque is limited.

When should I move from RU42 to RU66?

RU66 should be considered when a larger center opening, greater mounting rigidity or significantly higher dynamic and static load ratings are required.

Is CRBF2012AT automatically interchangeable with RU42?

It is a common dimensional reference, but drawings, hole patterns, load ratings, seals, accuracy, clearance and rotational torque must be compared before replacement.

Request a Reliable RU42 Cross Roller Bearing Quote

For accurate selection and pricing, provide the quantity, application, loads, moment arm, speed, duty cycle, rotating ring, accuracy, preload, seal type, lubricant and acceptable torque. Contact the LYDL engineering team for an RU42 drawing, model review, production lead time and export quotation.

Technical References and Citation Scope

1. THK, Cross-Roller Ring—Model RU Used as a dimensional and structural reference for integrated inner and outer rings, RU42 boundary dimensions and catalog load ratings.
2. IKO, CRBF Crossed Roller Bearings with Mounting Holes Used for comparison with CRBF2012AT and CRBF2012ATUU mounting-holed configurations.
3. ISO 281:2007, Rolling Bearings—Dynamic Load Ratings and Rating Life Used as the general reference for dynamic load-rating and bearing-life calculation principles.
4. ISO 76:2006, Rolling Bearings—Static Load Ratings Used as the general reference for static load ratings, equivalent static load and static safety evaluation.
5. ISO 492:2023, Rolling Bearings—Radial Bearings—GPS and Tolerance Values Used as a general reference for dimensional and geometrical tolerance terminology. Final RU42 tolerances remain subject to the approved product drawing.
6. ISO 15243:2017, Rolling Bearings—Damage and Failures Used as a reference for recognized bearing damage terminology, characteristics and possible service-related causes.

These references support terminology, calculation principles and dimensional comparison. They do not replace the final LYDL drawing, inspection agreement or application-specific engineering review.

Explore this bearing series

RU Series Integrated Cross Roller Bearings · Series dimensions and selection guide

Published RU model pages

RU85 · RU66 · RU42 · RU124 · RU148 · RU178 · RU228 · RU52 · RU28 · RU297