Ask a Design Engineer: Square Ball U-Joint


A recent LinkedIn question was posed regarding the Square Ball Universal Joint® and its mechanics. John Sweetwood, the bearing’s co-designer, answers the questions regarding pins, seals and cost in this post.

Rotational Force and Retaining Pins

The only function of the retaining pins are to keep the Square Ball central element from slipping out either end of the mouth when the assembly is in a relaxed state. The rotational torque is transferred/concentrated around the left and right opposing zones of the yoke’s ID (the mouth) to the adjacent cylindrical surfaces of the Square Ball central element, not the center of the yoke or the grooves in the Square Ball.

The assembly’s ability to handle loads was learned from the spherical plain bearings we manufacture. The motion is also very similar; the central element is simply oscillating within the cylindrical mouth of each yoke, much like the inner ring of a spherical plain bearing. A spherical plain bearing is used when a high load capacity is needed along with the ability to handle some operational misalignment.

For example, many hydraulic cylinders have spherical plain bearings in their rod ends. These bearings can withstand the large loads and changing angles when a hydraulic cylinder extends and retracts. They achieve the high load capacity through a large contact load zone between the inner and outer ring of the spherical plain bearing. This load zone spreads the pounds per square inch (psi) over a large enough area to keep the Mpa/psi low enough for the materials to perform well within their limits.

Needle bearings don’t do as well in high load environments because of their inability to create a large enough load zone. The needle bearing load zone is only as large as the line contact area between the length of the needle and the raceways. If the area of contact for each line of each needle bearing in the load zone is calculated, it will be smaller than the contact area of a like-sized spherical plain bearing. The smaller contact area will experience metal fatigue sooner than a larger contact area due to the higher Mpa/psi applied to the surfaces.


Since CCTY also manufactures ball joints for many in the performance ATV and UTV market, we have learned how to develop effective seals for exposed, harsh environments. Most of our ball joints are sealed for life and maintenance free. The seal for the Square Ball universal joint was not included in the video because it would have hidden the unique features of it. Each Square Ball universal joint has all of the moving elements protected by a seal containing grease.


The Square Ball u-joint design benefits from technology we have learned from decades of manufacturing our spherical plain bearing and ball joints. CCTY has a very good understanding of the materials to use, sliding surface finishes, material hardness, etc. that perform well in high pressure slide bearing applications.

The beautiful benefit of the Square Ball universal joint design is we already have the engineering know how, necessary machinery and manufacturing capacity resulting from the bearing products we already manufacture. So, fortunately, the cost of components isn’t as high for us as it would be for a company that doesn’t already have our engineering and manufacturing abilities. 

U-Joint Replacement

This design was inspired by linkage needed for steering applications; we know it serves them well. As to the trucks and PTO drive applications you mention, the functionality of these applications has yet to be tested. Keep in mind many of those applications are designed to operate at a minimal misalignment.

For applications that have slight misalignment there will be very little oscillating movement of the central element, it will simply transfer the torque. We will start testing these types of applications in the near future. Please keep reading our posts for those updates.

 >>>See the Square Ball Universal Joint in motion.<<<

See it in Motion