Nestable side laps “nest” atop the adjacent panel with a lip that can be screwed, or seam welded.  Interlocking side laps include a male lip that fits into the female lip and can be welded, or button punched.  Upon request, Interlocking deck can often be requested with an “added return” on the female lip that allows the deck to have a screw attachment.  Proprietary fasteners are also available.