I got tired of buying replacements for long bike rack holder as it would break every year or so and then never seem to be in stock.
This part is specifically designed for Axiom Streamliner Road DLX rack and Marin Ignacio bicycle. If you are trying to use this part for other designs you might want to print it to make sure that all the mounting holes align, and the angles are correct, specifically that the distance between rack mount and the frame is the same.
This design is still in prototyping stage, and I haven't put a lot of weight on the newly printed part, but I've been cycling with it for a few weeks and nothing seem to break.
This part should be printed on its side.