This is a bracket for the IKEA Sunnersta wall-mounted rail (https://www.ikea.com/us/en/catalog/products/30303722/) to be able to mount lights above its hanging containers. This allows it to become an indoor, pet-proof mini garden for herbs or other small plants. The bracket is designed to use 1/2" square or similar aluminum tubing for the top light bar.

The bottom hole is for an optional set screw. 1/4"x20 or similar tap required.