Small parts orders are where Di2 installations either come together cleanly or turn into a zip-tie mess, and the SM-EW90 mounting plate is one of those sub-$15 parts that quietly makes the whole system look factory. This is the hook plate that pairs with the CY9082 rubber band to hold an EW90-A (three-port) or EW90-B (five-port) external junction box against the underside of a stem. It's not glamorous hardware — it's a small plastic plate — but it's the correct Shimano-spec way to secure the junction so the E-Tube ports face rearward and the diagnostic port stays accessible.

The mounting plate itself is the piece with the hooks molded into it. The rubber band wraps over the top of the stem, hooks onto both sides of the plate, and clamps the EW90 junction box between the plate and the stem underside. Nothing threads into the stem, nothing gets adhered — it's a purely mechanical band-and-hook system that Shimano designed so the junction can be removed for service or firmware updates without cutting anything. If you've ever had to replace a junction box mid-season, you already know why that matters.

Worth knowing before you order: the CY9082 rubber band is a separate part number and is not included with this mounting plate. If your original band has stretched, cracked, or gone missing, you'll want to order both pieces together. This plate also only fits the EW90-A and EW90-B external junction boxes — it's not compatible with the EW-RS910 bar-end junction, the internal EW-JC130/JC200/JC304 frame junctions, or any of the newer 12-speed Di2 wireless-era hardware. Confirm your junction box part number before adding to cart.... Read More