Precision matters when it comes to bearing systems, and the unsung heroes behind optimal performance are often the smallest parts. Whether you’re assembling a high-speed spindle, industrial gearbox, or heavy-duty conveyor, accessories like locknuts, spacer, and shims play a crucial role in securing, aligning, and fine-tuning the setup. While bearings get the spotlight, it’s these support components that often determine the longevity, vibration resistance, and true performance of the system.
In this article, we’ll explore why locknuts, spacer, and shims are essential—not optional—components, and how selecting the right ones can transform a good installation into a great one.
Why Bearing Accessories Are Not Optional
Bearings don’t work in isolation. The surrounding parts dictate how well they perform. Locknuts, spacer, and shims help to:
- Keep bearings in position
- Maintain axial preload or clearance
- Reduce vibration and misalignment
- Simplify adjustments and future maintenance
Without proper accessories, even high-quality bearings can fail early due to excessive friction, heat buildup, or shaft movement. These small components are critical in applications ranging from machine tools to automotive hubs.
1. Locknuts: Securing Axial Position Like a Pro
Locknuts are used to secure bearings onto a shaft or in a housing. They’re designed to hold axial preload and prevent movement that could lead to slippage or misalignment. Think of locknuts as the final handshake between the bearing and its support system—they make sure everything stays in place under pressure.
Common Applications:
- Spindle assemblies
- Electric motors
- Gearboxes
- Agricultural equipment
Types of Locknuts:
- Slotted (KM-type)
- Threaded precision locknuts
- Self-locking variants with nylon or metal inserts
The type of locknuts used often depends on the application’s speed, load, and required precision. For high-speed spindles, precision-threaded locknuts are preferred due to their tight tolerances.
Creative Tip:
Pair locknuts with tab washers or locking clips to enhance their security without relying solely on torque. This prevents loosening during vibration-heavy operation.
2. Spacer: Aligning and Isolating with Precision
A spacer may seem like just a filler, but in reality, it’s a load-bearing, tolerance-defining component. In bearing systems, a spacer separates two bearings, ensuring the correct axial distance and helping maintain the required preload.
When to Use a Spacer:
- In paired bearing configurations (back-to-back or face-to-face)
- To isolate vibration between components
- To absorb differential thermal expansion
- To distribute axial load evenly
Using a poorly sized or poorly machined spacer can compromise the system. It can lead to uneven loads, excessive heat, or even bearing lock-up.
Common Materials:
- Aluminum for lightweight applications
- Steel for high-load or high-temp environments
- Composite materials for damping and insulation
3. Shims: The Fine-Tuning Specialists
While spacer sets the general geometry, shims are the surgical tools of the bearing world. These ultra-thin, precisely machined plates are used to make micro-adjustments in alignment, spacing, and preload.
Why Use Shims:
- Fine-tune preload in angular contact bearings
- Correct minor shaft or housing misalignments
- Adjust axial positions during assembly or service
- Maintain proper seal contact in housings
Shims are incredibly useful in retrofit situations or when tolerances need last-minute correction. Instead of remachining parts, just insert or remove a shim.
Pro Tip:
Always keep a shim kit on hand in your maintenance shop. It’s a low-cost, high-reward way to make in-the-field adjustments without delays.
How These Three Work Together
Let’s say you’re installing a pair of angular contact bearings in a high-speed electric motor. Here’s how you’d use locknuts, spacer, and shims together:
- Spacer goes between the two bearings to maintain preload distance.
- Shims are added behind the outer race to fine-tune preload after thermal testing.
- Locknuts are torqued on the shaft to hold the bearing pack in place without back-off.
The result? A tightly controlled bearing environment that minimizes vibration, extends service life, and boosts system efficiency.
Real-World Scenarios: Where Accessories Save the Day
1. High-Speed Machining Centers
A 0.01 mm misalignment in spindle bearings can ruin surface finish and tool life. With proper shims and spacer, you ensure axial precision and reduce dynamic imbalance.
2. Wind Turbines
Axial loads vary dramatically in turbine applications. Strong locknuts and preload-adjustable spacer configurations are critical to absorbing shock and wind-induced fluctuations.
3. Conveyor Systems
In long industrial conveyors, thermal expansion can shift bearing positions. Here, shims allow for on-site realignment, and locknuts secure the adjusted setting.
4. Automotive Hubs
Modern cars often use pre-assembled hub units. But in motorsports or modified builds, custom locknuts and spacer ensure the hub remains tight under cornering stress.
Mistakes to Avoid
❌ Using the Wrong Locknut Type
Some locknuts are designed for one-time use, while others can be reused. Know the difference and avoid reusing torque-sensitive models.
❌ Over-Stacking Shims
Too many shims can introduce compressibility and reduce accuracy. Stick to as few as possible, and always use high-quality stainless or hardened steel options.
❌ DIY Spacer Errors
Improperly machined spacer can cause misalignment or uneven loading. Always use ground or precision-turned components.
Innovative Trends in Bearing Accessories
As technology advances, even accessories are becoming smarter.
Smart Locknuts
Some locknuts now come embedded with torque sensors or RFID chips that record installation torque or monitor vibrational load.
3D-Printed Spacers
Rapid prototyping with additive manufacturing allows for custom-fit spacer solutions with embedded damping features.
Color-Coded Shim Kits
Manufacturers now offer shims in pre-sorted, color-coded packs, reducing installation time and human error.
Choosing the Right Accessories: A Quick Checklist
When selecting your locknuts, spacer, or shims, consider the following:
| Factor | Locknuts | Spacer | Shims |
| Load Rating | ✅ | ✅ | ❌ |
| Adjustability | ❌ | ✅ | ✅ |
| Reusability | Depends on type | ✅ | ✅ |
| Cost | Low | Medium | Low |
| Precision Impact | High | High | Very High |
| Material Choices | Steel, nylon | Steel, aluminum | Steel, brass |
Make your choice based on speed, load, maintenance needs, and available space.
Final Thoughts
Bearings are vital, but they’re only as strong as the components that support them. Accessories like locknuts, spacer, and shims provide the foundation for performance, longevity, and reliability. Skipping these components or choosing them carelessly is a fast-track to vibration issues, misalignment, and early failure.
So next time you’re selecting bearings, remember the small parts that make the big difference. Whether you’re building, repairing, or optimizing, investing in high-quality locknuts, using precision-ground spacer, and keeping a drawer full of shims isn’t just smart—it’s essential. Know More