Those are called rivets which are extremely durable and strong when installed correctly using a rivet gun, however, standard stainless bolts and nuts sourced from a local hardware store will work just as well.
I recently installed the aftermarket chrome interior package on my Mini 2 door coupe S. Prior to installation the carbon black interior felt dark and somewhat cheap. After installation the interior came alive. It appears much richer and bright and almost a different interior. It takes patience to install all of the pieces but it is time well spent. Highly recommended.
Lou Kirchner
Placed several orders with OutMotoring, F56 JCW Pro parts, front bumper kit for MINI GP R53. Shipping is always fast and all items arrived perfectly. Very happy and will continue ordering all my MINI needs from OM :)