Bicycle rear rack dropout adapter

I wanted to mount a rear rack on my bicycle, which did does not have eyelets on the dropouts nor is the frame appropriate for p-clamps (it's a bamboo frame).

Folks at the local shop had an idea to use a special nut designed to add a derailleur to old horizontal dropouts as an attachment point. However, this made the rack a bit closer to the rear wheel than I'd prefer—it prevented adding a rear fender.

These adapters attach to the rack and provide a bolt hole for the dropout mount. They seem sturdy enough for now, but I'm only commuting with a light load, and have only been using them in moderate temperatures for a short time. I'm planning on refining the design and eventually having a similar shape fabricated from steel, likely slightly thinner.

These are designed for a Bontrager Backrack Lightweight and the dropouts on a Bamboo Bicycle Studio frame.

(TODO: add images of the nut used and a photo of the rack mounted).