Designed for the Tortec Tour Ultralite Rear Rack and an old plastic box. Print out of PLA has worked so far for me.
This uses:
I printed with an 0.6mm nozzle & 0.3mm layer height, and no supports, but it's a simple chuky, functional model. You could do anything you like.
Box releases from rack in about 5 seconds, and it takes about 10 seconds to put on. I have tested it under moderate loads and speeds for the past couple of weeks.
Concept valid and could be adapted to fit random things to other racks.
The author hasn't provided the model origin yet.