I am in the process of replacing an old bathroom fan in a guest bathroom with a new Nutone ARN110LKVV. After running some new electrical and getting the old fan out, I finally got to the step where I attach the new fan metal enclosure to the joist. I am following the instructions, which tell me to use "appropriate fasteners." I have no idea what an appropriate fastener would be.
Moreover, the metal box being attached to the joist does not have any actual "holes" to screw through. They seem to be metal indentations, that don't seem like they're supposed to be screwed through.
This is a close-up of what one of those "identations" look like on the inside of the box, and this is a close-up of that same indentation from the outside.
Is there some sort of screw that's intended to go through the metal and into the joist? Or should I use a drill bit to drill through those indentations and into the joist, then use some sort of screw? The instructions have no guidance on what type of fastener to use.