U-style spring nuts are bent to resemble the letter U, which provides a tighter and more secure hold than J-shape nuts. They clip onto the edge of metal panels and provide a threaded mounting point. There is no need to tap threads into the panel and they are removable, allowing for easy assembly and disassembly.
https://www.grainger.com/product/Spring-Nut-U-Clip-On-4CUG3?searchQuery=4CUG3&searchBar=true