Aluminum Bottom Bracket Socket T47

T47 is the bottom bracket standard pioneered by Chris King and adopted by Trek (T47i, internal-bearing) and Pinarello (T47a, external-bearing), among others. The shell is 47 mm threaded with a 1.0 mm thread pitch; wider than BSA (33.7 mm at 1.37") which lets the cup house a 30 mm spindle without forcing the bearing inboard into the frame, where it traditionally lived in the BB30 era. The T47 cup is the answer to the ”want a 30 mm spindle without going press-fit“ question that came out of the BB30 / PF30 era.

The 1671 Aluminum BB Socket cut for T47 fits the cup's specific notch profile. T47's wide diameter means the cup OD is dimensionally different from any other BB family in the catalog; a standard 16-notch wrench won't fit at all, not just fit imprecisely. The dedicated socket is the only correct tool for T47 cup installation and removal.

T47 thread handedness

T47 mirrors BSA's per-side thread handedness: right-hand thread on the non-drive side, left-hand thread on the drive side. The split-handedness exists to prevent the drive-side cup from backing out under pedaling load; the drive-side spindle rotates in the loosening direction relative to a right-hand thread, so the drive side is left-hand threaded to make pedaling load tighten the cup, not loosen it. Chris King's ThreadFit T47 is the originating spec; Trek's T47i and Pinarello's T47a adopt the same handedness.

Carbon-shell T47 variants

Modern carbon frames; notably the Trek Domane SLR 9 AXS (2021+) and Trek's broader Domane / Madone T47 lineup; ship with bonded metal threaded inserts sized to T47. The bonded insert lets the T47 standard apply to a carbon frame without full-frame threading, and the BB tool doesn't distinguish between a metal-shell T47 and a carbon-shell-with-insert T47 (the engagement face is metal in both cases).

Compatibility

• T47 threaded BB cups (Chris King ThreadFit T47; Trek T47i internal-bearing; Pinarello T47a external-bearing)
• Carbon frames with bonded T47 metal threaded inserts
• Not for press-fit shells; the T47 designation requires threading

Specs

• Drive: 1/2" square drive (use with a torque wrench, ratchet, or fixed handle such as the Pro Socket Handle)
• Material: CNC-machined aluminum, red-anodized
• Notch fit: T47 outer profile
• Includes: the socket itself; pair with the Bottom Bracket Socket Retaining Tool for low-profile cup engagement

Built in Zreče

Unior has been forging hand tools in Zreče since 1919, and is the official technical partner of multiple World Tour and downhill teams. The T47 socket entered the workshop tool palette when the BB standard itself moved from boutique (Chris King's original spec) to mainstream (Trek Domane, Pinarello Dogma, BMC Roadmachine), and the aluminum body keeps the cup face mark-free on the carbon frames where T47 lives most often.

Pro tip from our mechanics

The T47 cup wants to be checked for cleanliness more thoroughly than a BSA cup, because the wider thread diameter means a small contamination; a fleck of frame paint, a dried grease deposit; translates to a worse thread engagement than the same contamination on a narrower thread. Wipe the frame's T47 thread with a clean rag before threading the cup, and inspect the cup's leading threads for shipping debris. The five seconds spent looking is what keeps the cup square in the shell on the first quarter-turn.

For the install / torque / thread-direction reference: Replace or clean your bottom bracket →.