This handle little 2-piece composite Cervelo MT-294A downtube mount allows you to secure a Shimano Di2 E-Tube EW-RS910 Internal Junction A box into the wiring port hole of the Caledonia 5 frameset. The two pieces clip onto the junction box, then snaps into the frame port hole once the internal wiring is connected. Many people find this preferable to using the EW-RS910 in the handlebar end and can make wiring simpler while reducing wires in the bar.