Children's surname

If a couple lives together have different surnames and have a child, what's the most common surname for the child?

Rivets

So, I have a thing that was attached to leather with rivets, and it came off. And I thought, maybe I can fix this myself, and I had a look around, and found out I really didn't know what I was doing.

I assumed because I can get to both sides, it was easier to get a rivet with two separate ends and tap it with a hammer, than to use a rivet-applying-device? Which seems to be a completely separate sort of rivet, but I couldn't figure out what the terminology was. Or is it just easier to use a... device anyway?

Does anyone know what I should be looking for?