That looks like a fake Optiparts plug (this is the real thing: Laser Lower Mast Plug). The code is right, though, so maybe it's just the picture that's wrong. But then they talk about waterproofing the rivet, which makes no sense for the lower mast.
Wherever you're buying the plug from, ask if the rivet is included, and if not, ask them to include one. You may have to first drill out the old one to measure the size from the hole, and remember that it needs to have a countersunk head.