Di2 wires need to exit the frame somewhere near the rear derailleur, and on Cervelo disc frames that exit point sits on the seat tube. The Seatube Open Di2 Grommet seals this port while allowing the wire to pass through, creating a weather-tight transition between the frame's internal cavity and the external wire run to the derailleur. The slot in the grommet wraps around the wire snugly enough to keep water and grit out but still permits wire movement during seatpost adjustments and frame flex under load.

Without the grommet, or with a damaged one, the port becomes a direct path for road spray into your frame interior. Water that gets in doesn't drain easily and sits around internal cable routing, electronic junction boxes, and bare carbon surfaces. Over time that leads to corrosion on metal components and potential contamination of bearings or electronic connections. A fresh grommet that actually seals is cheap insurance compared to diagnosing intermittent Di2 shifting problems or dealing with internal corrosion you can't see until something fails.

The rubber construction stays flexible across temperature swings and maintains its seal even after years of UV exposure and cleaning chemicals. Press-fit installation means no adhesive or hardware, just push the grommet into the port until it seats against the frame surface. If your original has cracked, hardened, or gone missing during a derailleur replacement, this OEM part restores the seal with the correct fit for Cervelo's port geometry. Compatible with all Cervelo disc brake models, though verify your specific frame uses this grommet style before ordering since Cervelo uses different grommets across their various entry points and frame generations.