I had one of these angle brackets lying around in the basement. It's the sort of thing that gets used to provide support for stairs or decks. I have no idea why I had it. Still, it was conveniently pre-drilled with small holes. All I needed to do was to add one big hole so it would fit on my bike axle. One half-inch drill bit later and a bit of neatening up with a Dremmel and we're set.