It’s almost certainly bolted on through holes on the bedframe. As for what size, you could measure the hole diameters and get ones that fit. Fitting a headboard to your bed couldn’t be easier. Most headboards come with struts. These struts screw into the back of the headboard and will fit neatly on to the back of the any standard size divan bed. Beaver Dam Inn, Beaver Dam Picture: Marks and screws from former headboard – Check out TripAdvisor members’ 27 candid photos and videos of Beaver Dam Inn.
Then you can neatly slide the headboard down the back of the Divan. They are held in place by two bolts that screw in the base at the back of the Divan. The screws that came with it fit perfectly into the back of the headboard. Now, if your intention is to screw the bottom of the headboard into the frame in the bed, then you need to purchase screws for that.