Bontrager Blendr to GoPro mount adapter
Trek bikes ship with Bontrager Blendr stem and bar bases that accept only Blendr accessories. This adapter slides into the Blendr base like an official mount and presents a standard three-finger GoPro interface, so a Cycliq camera, Outbound light or any GoPro-foot accessory can hang from the stock base. The Blendr slide is measured from your base and locked by the original screw, the GoPro fingers are 3 mm thick with 3.2 mm gaps and a 5.2 mm hole, and the body is 8 mm thick. Print it slide-down in PETG or nylon; the fingers need no supports.
Blendr bases have subtle differences between stem and bar versions, so a random download often sits proud or will not take the screw. Give SpeakCAD the measured slot width, depth and screw position, preview the adapter free in the browser, fine-tune it in the chat, then download the STL.
Design an accessory adapter with a Bontrager Blendr style slide 20 mm wide, 6 mm thick and 25 mm long with a 4.5 mm screw hole, and a three-finger GoPro mount on the opposite face with 3 mm fingers, 3.2 mm gaps, a 5.2 mm hole and 8 mm body.