Cross roller bearings, also called crossed roller bearings, are one of the most compact and rigid bearing designs used in precision machinery. Instead of using balls, they use cylindrical rollers placed at 90 degrees to each other in a V-shaped groove. This arrangement lets a single bearing carry radial load, axial load and moment load at the same time, something that usually needs two or three separate bearings.
Because of this efficiency, cross roller bearings are widely used in robotic joints, rotary tables, machine tool spindles, medical scanning equipment, and slewing platforms. But not every cross roller bearing is built the same way. The internal structure, the ring design, the presence of gear teeth, and the mounting method all change depending on the application. Choosing the wrong type can affect accuracy, load capacity, and service life.
In this guide, we will explain every major type of cross roller bearing, how each one works, and where it fits best. If you supply or manufacture precision bearings for industrial equipment, understanding these differences also helps when comparing cross roller bearing suppliers, which produce several of these designs for robotics and rotary applications.
How Cross Roller Bearings Are Classified
The easiest way to understand these bearings is by looking at how the inner and outer rings are built. Some series split the outer ring, some split the inner ring, and some keep both rings solid with mounting holes for direct installation. This single detail decides which side of the bearing can rotate and how the bearing should be mounted.
1. Split Outer Ring Type, Suited for Inner Ring Rotation
In this design, the outer ring is made in two pieces while the inner ring stays as one solid part. It is the original and most common cross roller bearing layout, and it works well when the inner ring is the rotating side of the machine, such as a rotary table shaft.
The RB Series Cross Roller Bearings represent the standard version of this type. They are widely used in machining center rotary tables, robot joints and precision indexing units where rigidity and inner ring accuracy matter most.
The RA Series Cross Roller Bearings follow the same split outer ring principle but with a thinner cross section. By trimming the wall thickness of both rings, RA bearings reduce weight and free up space, which makes them a common choice for compact robot arms, manipulators and lightweight rotating fixtures.
The SX Series Cross Roller Bearings also use a split outer ring layout and follow international standard sizing, which makes them easy to swap in as a drop-in replacement in equipment originally designed around this bearing family.
2. Split Inner Ring Type, Suited for Outer Ring Rotation
This is the reverse arrangement. The inner ring is split into two halves while the outer ring stays solid, which allows the outer ring to be the rotating part of the assembly. This layout also makes it easier to fine tune bearing clearance or preload during assembly, since adjusting the split inner ring changes how tightly the rollers sit against the raceway.
The RE Series Cross Roller Bearings are the standard example of this design, commonly used where the outer housing or flange needs to rotate rather than the shaft.
The XV Series Cross Roller Bearings work on the same principle in a smaller size range, with mounting holes built into the outer ring for direct bolt-on installation, plus metal anti rust rings fitted on both sides for added protection during storage and use.
3. Integrated Type With Mounting Holes, Suited for Both Rings Rotating
Some applications need both the inner and outer ring to handle rotation and load with equal accuracy. For this, the rings are kept solid rather than split, and mounting holes are machined directly into both rings so the bearing can be bolted straight into the housing without a separate adapter.
The RU Series Integrated Cross Roller Bearings are built this way, which shortens shaft length and cuts machining costs since no separate housing design is required.
The XU Series Cross Roller Bearings and XSU Series Cross Roller Slewing Bearings follow the same integrated, mounting hole design in larger bore sizes, often sealed on both sides, and are common in rotary tables, medical scanning equipment and direct drive motor platforms.
The VU Series Cross Roller Bearings belong to this same family of solid ring, bolt on bearings, offering a lighter weight option for rotary platforms that still need strong moment load capacity.
4. Crossed Roller Slewing Ring Type
Once the bore diameter grows large enough, cross roller bearings start to function as slewing rings, meaning they support and rotate a heavier structure such as a turntable, antenna mount or solar tracking platform rather than just a shaft. These are still built on the same crossed roller principle but scaled up for larger loads and diameters.
The XA Series Cross Roller Bearings and XI Series Cross Roller Bearings, along with the XSA Series Cross Roller Bearings and XSI Series Cross Roller Bearings, fall into this slewing ring category. They are typically chosen for rotary stages, precision turntables and automation platforms where a wide diameter and steady load distribution are more important than compact size.
5. Cross Tapered Roller Bearings
Not every cross roller bearing uses cylindrical rollers. Some use tapered rollers instead, arranged in two rows at right angles rather than a single crossed row. This geometry spreads the effective bearing width far beyond the physical size of the bearing, giving it an exceptionally high resistance to overturning moment.
The XR / JXR / BFKB Series Cross Roller Bearings are the tapered roller version of this design, mainly used in large machine tool tables, vertical lathes, boring mills and heavy-duty rotary platforms where tilting resistance under load matters more than compactness.
6. Ultra-Thin and Compact Cross Roller Bearings
Where space and weight are the biggest constraints, manufacturers reduce the wall thickness of the rings to the practical minimum. These bearings keep the same load handling ability but in a noticeably slimmer cross section, which suits collaborative robots, small rotary joints and portable precision equipment.
The CRBT / RAU Series Ultra-Thin Cross Roller Bearings and the dedicated RAU Series both fall under this category, offering a mounting hole version of the thin RA design for applications that need both a slim profile and simple bolt-on installation.
7. Harmonic Reducer Cross Roller Bearings
Harmonic drive reducers, widely used in robot joints, rely on a dedicated rigid bearing built into the reducer housing itself. These bearings still use the crossed roller structure, with a split outer ring and integrated inner ring, but are sized and named to match specific harmonic reducer models rather than general machine applications.
The CSG / CSF Harmonic Reducer Bearings and SHF / SHG Harmonic Reducer Bearings both belong to this category, and are common replacement components when servicing robot arm reducers or building custom harmonic drive units.
How to Choose the Right Type
Start by identifying which ring needs to rotate in your machine. If the shaft or inner side rotates, a split outer ring type such as RB, RA or SX usually fits. If the housing or outer side rotates instead, RE or XV are the better starting point. When both rings need equal rotational accuracy, or when you want to avoid designing a separate housing, the integrated mounting hole types like RU, XU, XSU or VU are usually simpler to work with.
For larger turntables and platforms, look toward the slewing ring types such as XA, XI, XSA and XSI. If your application involves very high overturning moments, such as a machine tool table, the tapered roller XR, JXR and BFKB series are built specifically for that load pattern. And if you are sourcing a replacement bearing for a harmonic drive reducer, the CSG, CSF, SHF and SHG series are sized to match those units directly.
Common Applications
Industrial robot arms and joints, where compact size and high rigidity matter most. Rotary tables and indexing units on CNC machines and machining centers. Harmonic drive reducers used throughout robotics and automation. Solar tracking systems, antenna mounts, and rotary platforms using slewing ring types. Medical imaging equipment and precision measuring instruments that need smooth, accurate rotation.
Final Thoughts
Cross roller bearings cover a wide range of internal structures, and the right choice depends on which ring rotates, how much space you have, and how the bearing will be mounted. Split outer ring types like RB, RA and SX suit inner ring rotation, split inner ring types like RE and XV suit outer ring rotation, and integrated mounting hole types like RU, XU, XSU and VU simplify installation when both rings carry load. Larger slewing types, tapered roller designs and harmonic reducer bearings each solve a more specific engineering problem.
If you are trying to match an existing bearing or specify one for a new design, LYDL Bearing produces all of these series and can help confirm which structure fits your rotation direction, load pattern and available space.
