Boarding step
Lost Parent-
From your original post I sense that you want to duplicate this step for your own boat. If that is true, I offer you this alternative solution:
The pictures below are a step that I built for my own boat and I've built two others for sailing buddies. It is a simple board with grooves for water run-off and decoration, and is held by lines that can be adjusted for length for an individual boat if needed. I glued a piece of leather on the edge of the board that faces the hull for scratch protection.
Time to build was minimal- just one board, four holes, a few grooves and you are done. Materials are just a board, about seven feet of 1/4" or 5/16" line, and two clips, a piece of leather, and some exterior polyurethane. Total cost was under $15. It will clip onto lifelines, stanchions, or a perforated toe-rail anywhere you need it. It stores in a fraction of the space required for your pictured step, and you don't need to mount clips to the deck that you could stub your toes upon.
I use this for getting down to floating docks, and everyone who has used it thinks it looks and works great. The step you have pictured looks to be more solid, but although my step will move, nobody has ever fallen off of it.
Your original question regarding the hardware- it looks like standard boarding ladder hardware for removable ladders. I had one on a previous boat and it had that style of hook and plate.