Universal joints (U-joints) are workhorses of mechanical power transmission. They connect two shafts that may not be perfectly aligned, allowing torque and motion to transfer reliably. While their basic function is straightforward, the way a U-joint connects to a shaft—the bore configuration—makes all the difference in performance, installation, and durability.
Belden Universal offers plenty of standard bore configurations to choose from, as well as possibilities to customize bores. And while our experienced sales and engineering teams are happy to advise, we thought a quick rundown of the most common bore configurations with some basic facts cannot hurt.
Here’s a breakdown of the most common bore styles you’ll encounter.
1. Solid Hub
What it is:
A universal joint without any bore at all. Instead, it comes as a solid hub that can be custom-machined.
Where it’s used:
For specialized or OEM applications that require customized bores not covered by any industry standards.
Pros:
- Maximum flexibility for custom machining
- Can be adapted to unusual shaft sizes or shapes
Cons:
- Requires extra time and machining costs
2. Plain Bore
What it is:
A smooth, round bore with no keyway, setscrew, or special features.
Where it’s used:
For low- to moderate-torque applications, often paired with adhesive, setscrews or pinned connections.
Pros:
- Simple, low-cost option
- Can be re-bored or modified easily to include pin bores or setscrews
- Standard bore sizes are available for common shaft diameters.
Cons:
- Less secure against slippage without additional retention
3. Bore with Keyway (and Setscrew)
What it is:
A bore with a slot (keyway) cut inside, paired with a matching key in the shaft. This prevents rotation between the shaft and joint hub. A setscrew on top of the key provides axial retention of the shaft.
Where it’s used:
High-torque applications in pumps, conveyors, and industrial drives, for example.
Pros:
- Excellent torque transfer
- Minimizes risk of slippage
Cons:
- Requires a shaft with a key seat / keyway
- Slightly more complex installation
Hex Bores
What it is:
A bore with six straight sides of equal length and angles. This prevents rotation between the shaft and joint. They’re simple to machine and less prone to rotational slippage than round shafts without keys.
Where it’s used:
High-torque applications in pumps, conveyors, and industrial drives, for example.
Pros:
- Easy to assemble/disassemble
- no need for keyways
Cons:
- Less precise than splines
- can concentrate stress at corners
Square Bores
What it is:
A bore with four equal sides at 90° angles. This prevents rotation between the shaft and joint. They’re robust and easy to make but can be more prone to stress concentration.
Where it’s used:
They’re often used where simplicity and ruggedness matter more than high rotational speed.
Pros:
- Tough and simple
- great for slow-speed heavy-duty applications
Cons:
- High stress at corners
- less balanced at higher speeds
5. Spline Bore
What it is:
A bore with internal teeth (splines) that mate with matching splines on the shaft.
Where it’s used:
Automotive driveshafts, agricultural equipment, and heavy machinery, for example.
Pros:
- Handles very high torque loads
- Allows for axial movement (sliding spline) in some designs
- Very precise, low backlash
Cons:
- Requires splined shafts
- More expensive to manufacture
6. Thread Bore
What it is:
A bore with female thread machined to accept threaded shafts.
Where it’s used:
Applications that only rotate in one direction and do not require orientation of shafts during installation.
Pros:
- Easy to install and self-securing, if rotation is only in one direction.
- No play or slippage
Cons:
- Requires a threaded shaft
- Does not allow for bi-directional rotation.
7. Clamp Hub (Split hub)
What it is:
A bored hub with a split and clamping bolts that tighten the split hub around the shaft, securing it without damaging the surface.
Where it’s used:
Robotics, precision machinery, and motion control systems, for example.
Pros:
- Strong, concentric grip
- No shaft damage
- Easy to remove and reinstall
Cons:
- Bulkier than setscrew bores or other configurations
- Higher cost
Picking the Right Bore for the Job
When choosing a universal joint, the bore configuration is as important as the joint type itself. Think about:
- Torque capacity → Keyway and spline (alternately square or hex) bores handle heavy loads.
- Ease of installation → Setscrew and clamp hubs are quick and user-friendly.
- Precision needs → Clamp hubs excel in applications where alignment matters.
- Customization → Solid and plain bores are adaptable when nothing off the shelf fits or require customized bores not covered by any industry standards.
The right choice ensures your U-joint isn’t just a connector—it’s a reliable link in the power transmission chain. Our experienced sales and engineering teams are happy to advise when it comes to the best fit for your application. You can contact us HERE. Our quote request forms can also be helpful. Click for the SINGLE, DOUBLE, or DRIVESHAFT versions.
