Understanding Ball Bearings: 5 Common Questions Answered

Ball bearings are everywhere — in cars, skateboards, electric motors, and even hard drives. Though they may seem simple, they play a critical role in reducing friction and supporting rotating components. If you've ever found yourself confused about how ball bearings work or which type to choose, you're not alone. Let's dive into five common questions and explore their answers in depth.

1. What is the difference between sealed and open ball bearings?

When people talk about ball bearings, they often mention whether they’re sealed or open. This distinction isn’t just about appearance — it affects performance and maintenance.

Open ball bearings are exposed to the environment, allowing for easy inspection and lubrication. They’re ideal in clean environments where dust or debris is not a concern, such as inside a sealed gearbox or in applications where frequent maintenance is possible.

Sealed ball bearings, on the other hand, come with rubber or metal shields that keep out contaminants like dust and moisture. This makes them perfect for harsher environments or installations where maintenance access is limited. However, the trade-off is that you can't easily re-lubricate them, and once the grease degrades, the bearing will need to be replaced.

Choosing between the two comes down to your application's environment and how often you can service the bearing.

2. How do I know what size ball bearing I need?

Size matters — especially when selecting a bearing. But it’s not always clear how to determine the right dimensions. Fortunately, most ball bearings follow standard sizing based on three main measurements: inner diameter (ID), outer diameter (OD), and width (W).

You’ll typically find these measurements etched onto the bearing itself or listed in the equipment manual. If not, a caliper can help you measure the shaft (for the ID), the housing (for the OD), and the space available (for the W).

Bearings also come with a standardized part number system. For example, a 6202 bearing tells you the series, size, and type. Once you know this system, finding a replacement becomes much easier.

3. Why are my ball bearings making noise?

A common concern among users is unusual noise from ball bearings. If your equipment starts humming, grinding, or clicking, it's a sign something's wrong.

Dry bearings — those that have lost lubrication — often create a high-pitched whining or screeching sound. Contaminated bearings — with dirt, dust, or metal particles — tend to grind. In more serious cases, a bearing that has begun to fail mechanically might produce knocking or clicking noises due to pitted races or cracked balls.

To fix the issue, check if the bearing is sealed or open. For open bearings, cleaning and re-lubrication might resolve the problem. But if the bearing is sealed or shows signs of wear, replacement is often the safest route.

4. Can I use the same ball bearings for high-speed and low-speed applications?

Ball bearings are not one-size-fits-all. Different applications demand different tolerances, materials, and designs.

High-speed applications — such as electric motors or turbines — require bearings with precision construction, low friction seals, and often ceramic balls to reduce heat and wear. Look for ABEC-rated bearings for these uses, as the higher the ABEC rating, the tighter the tolerances.

Low-speed applications, like conveyor rollers or casters, don't need such high performance. Standard steel bearings will do just fine, and there's no need to invest in high-speed variants unless the load or environmental conditions require it.

Always consider both the speed and the load of your application before choosing your bearing.

5. How often should ball bearings be lubricated?

Lubrication is the lifeblood of any bearing. Without it, friction increases, leading to wear, overheating, and failure.

The frequency of lubrication depends on several factors: the operating environment (dusty, wet, or clean), speed of rotation, load on the bearing, and whether it's sealed or open.

• For sealed bearings, no maintenance is typically needed — they’re pre-lubricated at the factory.

• For open bearings, re-lubrication could be required anywhere from every few weeks to several months, depending on usage. Some heavy-duty applications even require daily lubrication.

Using the correct type of lubricant — usually a high-quality grease or oil — and applying it properly can dramatically extend bearing life and reduce downtime.

Final Thoughts

Ball bearings may be small, but they carry a big responsibility. From knowing whether to use sealed or open bearings to understanding lubrication schedules and sizing methods, the more you know, the better you can optimize your machinery. Whether you're a DIY enthusiast or an industrial engineer, answering these questions helps you make smarter decisions and keep your systems running smoothly.

If you’ve faced challenges with ball bearings or found clever solutions, share your thoughts with us. The world of motion is full of learning opportunities, and every tip helps.