What is a Finish Bore Sprocket Hub?

Posted on June 30, 2026 in FAQ, How To

A maintenance technician is standing next to a down conveyor with a worn sprocket in his hand. The chain size is right. The tooth count is right. The bore looks close. But when he goes to install the replacement, something is off. The sprocket does not sit on the shaft the same way, the set screw location is different, and the chain alignment is not where it needs to be.

That is where the sprocket hub matters. On a Type B finish bore sprocket, the hub is the raised section on one side of the sprocket, that is smaller then the tooth plate OD, that gives the sprocket more contact area on the shaft. It is not just extra metal. The hub helps the sprocket mount securely, stay aligned, and transfer power from the shaft to the roller chain drive.

What Is a Type B Sprocket?

A Type B sprocket is a roller chain sprocket with a hub on one side. This is one of the most common sprocket styles used in industrial chain drives because it provides a stronger and more secure mounting surface than a flat plate sprocket.

When a Type B sprocket is sold as a finish bore sprocket, that means the bore has already been machined to a finished shaft size. Most finish bore sprockets also include a standard keyway and set screws, making them ready to install without additional machining.

Why Is the Hub Important?

The hub is important because it helps the sprocket hold onto the shaft correctly. Without enough hub length or shaft contact, the sprocket may be harder to secure, easier to misalign, and more likely to cause chain wear or vibration.

On a finish bore sprocket, the hub also provides space for the keyway and set screws. The keyway helps transfer torque between the shaft and sprocket, while the set screws help hold the sprocket in position. Together, the bore, keyway, set screws, and hub help create a dependable connection between the shaft and the roller chain drive.

What Can Go Wrong with the Wrong Hub?

If the sprocket hub does not match the application, several problems can show up. The sprocket may sit too far in or out on the shaft, causing chain misalignment. The set screws may not land where they need to. The sprocket may wobble, loosen, or wear the chain and sprocket teeth faster than expected.

That is why matching more than just the chain size matters. When replacing a sprocket, you should look at the chain number, tooth count, bore size, keyway size, hub style, hub diameter, and overall width. A sprocket can look close and still be wrong for the application.

Why Choose a Finish Bore Type B Sprocket?

A finish bore Type B sprocket is a practical choice when you already know your shaft size and need a sprocket that is ready to install. Since the bore, keyway, and set screws are already finished, it can save time compared to buying a plain bore sprocket and sending it out for machining.

For maintenance teams, farms, manufacturers, conveyor systems, and repair shops, that time savings can be a big deal. A finish bore sprocket can help reduce downtime, simplify replacement, and get equipment back in service faster.

Need Help Matching a Finish Bore Sprocket?

At MDS of Michigan, we help customers match finish bore sprockets by chain size, tooth count, bore size, keyway, hub style, and application. If you are replacing an existing sprocket, a photo of the sprocket and shaft details can often help us point you in the right direction.

You can also use our standard keyway size chart to help confirm the correct keyway size for your bore.