Clean internal routing means sealing the entry points where wires pass into the frame. The SM-GM01 grommets are the finishing detail that keeps water, grit, and road spray from following your Di2 cables inside the tubes. They're small rubber inserts sized for 6mm circular frame holes—the standard entry point on most frames designed for electronic shifting. A pack includes four grommets, which typically covers a complete build with spares left over.

The grommets seat into the frame's cable ports and grip the EW-SD50 wire as it passes through. This does two things: it creates a weather seal at the frame opening, and it holds the wire in place so it doesn't rattle around inside the frame or get pulled when you turn the handlebars. Without grommets, you're relying on friction alone to keep wires positioned, and you're leaving an open path for contamination to enter the frame.

Frame manufacturers generally spec either 6mm round holes (SM-GM01) or 7x8mm oval holes (SM-GM02) for their Di2 routing. If you're not sure which your frame uses, check with the manufacturer or measure the opening before ordering. The wrong size won't seat properly and defeats the purpose of using a grommet in the first place. Having the correct grommets on hand before starting a Di2 build saves the frustration of discovering you need them halfway through the installation.