When converting to eTAP from a standard cable-based setup, holes are left in the down tube, seat post tube, the bottom bracket, and the rear derailleur cable exit. The down tube holes, seat post holes, and the bottom bracket hole can let water and debris enter the bottom bracket contaminating the bearings and flooding the Di2 cable connections.
In the Kit: 7 mm seat post plug, 6 mm Di2 cable hole plug, two (2) down tube shift cable plugs, a rear derailleur cable exit plug, and a Nylon bottom bracket cap.
The bottom bracket cap replaces the plastic cable guide that falls out when the shift cables are removed. The rear derailleur plug replaces the cable grommet in the rear which is mostly cosmetic. The down tube plugs and bottom bracket cap form a water tight seal for the bottom bracket that will prevent contaminants from entering the inside of the frame.
Weight: < 3g
When installing the bottom bracket cap, always attach it from the rear of the bike first (hook back, clip front). Gently clip in the front using your thumb as shown in the pictures. If not installed correctly, the tab can break. This is due to the angle the hole is cut in the frame.
To remove the BB cap, use the small ridge in the rear center of the cap, to pop off the rear of the cap first. This is the opposite direction used in the installation. The front of the cap faces the front of the bike and is indicated by arrows on the inside.