Specialized OSBB – Engineering Guide

Posted on 8 Comments


A question that crops up frequently is with regards to Specialized’s OSBB bottom bracket and what size it is exactly.

The short answer is OSBB comes in 3 variants which are all called OSBB. 46×61, 42×68 and 46×73. A summary table is below, with the detailed drawings below that.

Variant (Diameter x Width) (mm)ApplicationDescription
46 x 61RoadFrame tolerances are the same as PF30. It is extremely narrow
42 x 68RoadThis has exactly the same dimensions as BB30 and is designed for 6806 or 61806 bearings and a 30mm axle.
46 x 73MTBThis the same as PF30 MTB

46 x 61mm OSBB Road Applications

This is a shortened version of PF30. It uses the same type of cups to encapsulate the bearings which then push into the bike frame. The bearings are usually 6806. it was designed for 30mm axles.

This is technically a poor standard because the bearing stance is very narrow. It lends itself to quite a lot of flex which would require significant material in the bike frame to regain the lost stiffness. OSBB in this guise has the narrowest stance of any modern BB standard.

OSBB Shell
OSBB 46 x 61

42 x 68mm OSBB Road Applications

This is the same as BB30. It uses two smalley VHM 42 circlips to hold in a pair of 6806 bearings. It was designed for 30mm axles. A schematic of this is shown below

BB30 Shell

The only real quirk of this against BB30 is the use or non use of circlips. Some OSBB bottom brackets have an integrated lip in the bottom bracket and do away with the Smalley VHM 42 circlips.

42 x 73mm OSBB MTB Applications

This is the same as PF30 MTB.

Cranksets and OSBB

If a 30mm crankset is being used, 6806 bearings should be used with inboard bearings. The use of 6806 bearings in an outboard sleeve configuration is not recommended due to the small width of the bottom bracket.

If a different crankset is used such as Shimano or SRAM GXP. then a Hambini Bottom Bracket with 6805 based bearings can be used.


8 thoughts on “Specialized OSBB – Engineering Guide

  1. Hi, what ceramic bottom bracket bearing would you recommend to replace the standard ceramic speed bearing in my S-Works Venge

    1. You would only be able to fit 6806 bearings if you are using a 30mm crankset. If you are using a 24mm crankset then different options are available. In both cases I would not recommend ceramic bearings.

  2. Hi ! Great product Hambini ??✅I’ve been racing on my Canyon Aero SLX For the lat 2 years ,fantastic ?? Now I want to upgrade my Specialized SL 6 Tarmac with A threaded bottom brackets.Which one will you recommend.Thanks for your help and great product ?✅?

  3. Hi, what Hambini BB can you offer for the Specialized OSBB 61 version please? I have the S Works cranks installed and currently the plastic cups, which got loose with the time now…
    I had a look but seems that you offer only the 68mm home version.

    1. They are not that popular anymore but I do make them to order.

      1. Thanks, could you possibly dropp me me an offer for the osbb61 bb please?

        1. Same question… I need an OSBB61 for an SWorks Tarmac… what is the part number and price?

          1. if you use the contact form, you can start a custom request.

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