Is this the folding leg of a removable bench seat?
The bottom of the seat is wood. If this is a wood screw, then the way we fixed this issue was to do the following.
1) remove the upholstry on the seat. There are staples inside of the trim on the underside. Use a small common screwdriver or a staple puller.
2) remove the cushion.
3) using a 316 stainless machine screw (bolt), nyloc (locking) nut and washers, through-bolt the mounting hardware.
4) give the seat base a good coat of poly, (or fabricate a new one (chances are the wood screw pulled because the plywood is compromised with water and rotting).
5) re-install the cushion.
6) use stainless steel staples to re-upholster the seat.