Ask A Stupid Question - ask Bikerumor your bicycle maintenance and tech questions and we'll find the answer

We know, there’s no such thing as a stupid question. But there are definitely some questions too embarrassing to ask your local shop or riding buddies. This is the first in a weekly installment where we get to the bottom of your questions – serious or otherwise. 

Char asks – What the hell does BSA stand for?

In terms of the BSA we often see associated with bicycles, specifically bottom brackets, it originates from the Birmingham Small Arms company. Back in the day when manufacturing was fairly limited to a few large entities, the Birmingham Small Arms Company Limited started out with the manufacture of guns in 1861 and ended up branching out to bicycles in 1880. Bicycle parts soon followed in 1893. While we struggle today with standards for the type of bottom bracket used, back then there weren’t even standards for thread pitch and sizing. Eventually the threading that B.S.A. settled on for their bikes was accepted as B.S.C. or British Standard Cycle, which essentially was absorbed by ISO (International Organization for Standardization) sizing.

The short answer to your question is that when you see BSA in terms of a bottom bracket, it refers to a 68 or 73mm shell with 1.370/1.375″ x 24 TPI threads and a left hand thread on the drive side cup. These days, BSA, ISO, and English are used interchangeably to refer to what is now considered to be a standard threaded bottom bracket shell or bottom bracket.

Qwerty wonders –  How do I convert an English Ultegra 6800 crank to fit a BB30 Frame?

In this case, you don’t do anything with the crank so much as change the bottom bracket or use an adapter. There are a number of options from threaded sleeves that are pressed into BB30 frames that English BB cups then thread into like this one from SRAM, to complete bottom bracket assemblies like the Praxis Works Conversion BB or BBInfinite that install into a BB30 bearing bore (without BB30 bearings) and are stepped down to fit the 24mm spindles used on Hollowtech II cranks like the Ultegra 6800. The third option is a simple bearing adapter like those from Wheels Manufacturing that sit inside the bearing of your BB30 bottom bracket and reduce the inner diameter and increase the width to fit the needs of the crank.

In my opinion the complete bottom bracket assemblies are the best option in terms of durability and creak-free operation, though the bearing adapters are probably the easiest to use from a home mechanic’s point of view.

Got a question of your own?  Click here to use the AASQ form, or find the link under the Contact menu header up top anytime a question pops into your mind!


  1. Please note that BSA BBs have a left hand thread on the *drive* side (right hand side), not on the non-drive side as stated above. No BB I’ve seen or heard of has a LH thread on the left side, but Italian threaded BBs (36x24F) have a right hand thread on the right hand side too; these are rare now though. There are other, more obscure, threaded BBs out there too, but all except BSA (and maybe Italian) are extinct on new bikes.

    • You are correct about the threading and woe be to anyone that tries to unthread a fixed cup the wrong way. That never ends well.

      BR, you should correct your article quickly and/or hire satanas.

    • Italian is still alive and well, much to my chagrin. Most (no pun intended) Pinarellos for sure, and I’m pretty sure the Italian made Colnagos still.

      • NDS is always normal threaded, partially because that’s the correct way it should be threaded, and partially because that’s the adjustable side for cup and cones, so adjustment is always the same.

  2. Don’t forget that, perhaps most famously, BSA was into the motorcycle business until that ultimately led to their demise in the 70’s (if memory serves right?)

    • Raleigh bought up BSA bicycles. BSA bought up British motorcycling marques like Raleigh did with British cycling marques. Poor quality relative to Japanese imports led to their demise, just like the rest of British motoring.

  3. Italian bb standard is still found on pinarello, some Colnago, carrera and custom made frames. These ere the only threaded bb’s still found on new carbon bikes. I’ve not seen a bsa specced carbon frame for quite some time. Most are some sort of stupid press fit system

  4. Those lucky enough to have a BSA threaded shell can fit up to 30mm crank spindles with the appropriate bearing cups.

    On carbon bikes, most BB shells are aluminum inserts anyway, so why not use BSA shells instead of press fits anyway? Regardless of cup diameter.

  5. Why don’t they just thread the outside of BB30 bearings and thread the bicycle so we can just screw them in like 386EVO? That seems like it would solve pretty much every problem. There would need to be some notches on the bearing for a tool to purchase for tightening but that’s not hard.

  6. I am just waiting for the Product Managers at Scott to finally admit press fit sucks and let their engineers develop a new frame with threaded BB. Why do they cling to to Press fit? Is it an ego thing?
    I would love to ride the new Spark, but not with a press fit.

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