Learn About Threaded Bottom Brackets

The bottom bracket on your bike allows the crankset spindle to move freely within the frame. When you first purchased your bike, it already included a bottom bracket. However, if you want to take your performance to the next level, you should look into changing it. Although factory bottom brackets get the job done, they won’t give you that extra edge that you might want, whether you are a competitor or you simply want to increase your performance on the next ride.

When buying a bottom bracket, threaded brackets me be the type that your bike needs. Here’s more information about these brackets:

Different Types of Threaded Bottom Brackets

As mentioned above, the bottom bracket is the connection point between the crankset spindle and your frame on your bike. The bottom bracket consists of a bearing on each side of the frame and (usually) cups to hold the bearings in place in the bottom bracket shell. Each bike is built to allow for a certain type of bottom bracket. So, if your bike is built for threaded bottom brackets, this is the type that you need to buy when you make an upgrade. Here’s a look at the different types of threaded bottom brackets:


BSA is actually short for “Birmingham Shell Arms”, and this is one of the types of bottom brackets your bike might need. Threaded brackets labeled as “BSA” may also be called by other names, including English Threaded, BSC, BC, ISO, British, and Euro. These threaded bottom brackets use a special shell that has threads on the inside of it. These threads are designed to hold the threaded cups and bearings that make up the bottom bracket. The bottom bracket cup will usually have thread specification of 1.37″ x 24 threads per inch or 34.88mm diameter. The diameter of the inside of the shell is usually around 33.7mm.


Italian threaded bottom brackets use the standard of 36mm x 24 threads per inch. Another difference in the Italian threaded bottom bracket is that both sides of the bracket are right-hand threaded. You should note that not all bikes that were made in Italy will use this type of standard. Definitely check with the manufacturer. The most common frame to use an Italian Threaded bottom bracket is Pinarello.

English Dub

These are brackets that are sometimes referred to has having English threading, or it may be abbreviated to ENG. These use the standard of 1.37” x 24 threads per inch and are also about 34.8mm in diameter. Also note that the left side, or the non-drive side, uses right-hand threading, which is standard for English products. This means that it will tighten in the clockwise direction. The drive side uses a left-hand thread and will tighten in the counterclockwise direction. The shell itself has about a 33.7mm diameter. The difference between the BSA and the English DUB is that the bearing is larger in the English DUB to allow for the larger DUB crank spindle.

English 30

The English 30 is similar to both the BSA and the English DUB. It has a standard 1.37” x 24 threads per inch and tightens the same as the other English bottom brackets. The difference here is that it uses a larger diameter bearing to allow for crank spindles with a diameter of 30mm. The bearing is the same size as the English DUB, but the dust covers are slightly larger in diameter.


This is also a common type of thread standard that you might encounter. In this style, the standard is 47mm diameter x 1mm pitch. The non-drive side is right-hand threaded, which means that it gets tighter in the clockwise direction. The drive side is left-hand threaded, which means that it gets tighter in the counterclockwise direction.

When deciding to update your bottom bracket, you certainly have a lot of choices. If your bike is built to accept threaded brackets, it will be one of those types that you need to buy.

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