bailer installation

I plan on installing a new bailer on an old laser. I have the brass cockpit bushing and a new bailer kit. The kit comes with the bailer, the o rings, rubber stopper, the screw and a plastic screw plug/fastener. It also comes with a tiny black square with one surface looks like peel and stick. This shows up in the web site pictures of the kit for purchase by various vendors. I know how to do the istallation, but I do not know what this little square is for. Does anyone know what it is?

they use it as a gasket where the bailer screws in to the hull

paxfish nailed it.. You are supposed to drill the hole, insert the plastic screw anchor (aka drywall anchor) and then put the black square on top of that, and screw thru it to seal it. Most people leave it out and use silicone/marine caulk instead..