these guys - they are all over the car holding things together; i just had a bunch laying around from all the parts i've stripped off to save weight. i presume they come in various sizes; i had enough of the proper size.
https://www.belmetric.com/metal-hardware-c-12_128_130/ns35ylw-speed-clip-sheet-metal-nut-p-717.html?zenid=he1fcgbg0rop921fapskkr4pe3