Shimano Di2 junction box holder for 31.8 mm handlebar
The Shimano SM-EW90 Di2 junction A normally hangs under the stem on a rubber band, where it rattles and gets pulled by the bar bag straps. This holder clamps a 31.8 mm handlebar next to the stem and cradles the junction box in a snug pocket with the button and charging port facing the rider, and a 3 mm slot at each end for the E-tube wires. The clamp closes with one M5 bolt, the pocket walls are 2 mm with a 0.3 mm clearance, and a small ramp lets the box snap in. Print it on its side in PETG.
Junction boxes differ between the three-port and five-port EW90 and the newer EW-RS910, so a downloaded holder often does not fit at all. Measure yours, tell SpeakCAD the body size, bar diameter and wire exits, preview the holder free in the browser, refine the snap in the chat, then download the STL.
Design a handlebar holder with a 31.8 mm split clamp and one M5 bolt, a pocket 44 x 20 x 11 mm with 2 mm walls and 0.3 mm clearance for a Shimano Di2 junction box, a 3 mm wire slot at each end and a 1 mm snap ramp.