Thanks for the help guys I will have to check out these answers. Have to say a few are more helpful then the others. When I first got my boat my engine locker lock was missing so that might be what the nut is from before they put a new one on their. I will also have to check the fuel pump. I will let everyone know. Also no power turn's.
Try the Part ID app. Take a picture and it will tell you what the part is. If you get too many possibilities, you go to the "additional information" line and type in "found in a bilge of a boat."
It works great when I'm working on my motorcycle and I have parts left over.
If you have parts left over, then you did the job correctly...
What are the actual dimensions, placing a ruler next to the parts when taking a picture helps the viewer establish scale. They appear to me to be from the same place, I suspect the nut held the wire part onto something. The wire looks like it is could be some sort of grab handle for two fingers to pull on or as other have said some sort of hose retainer that the nut would hold to a stud somewhere on the engine or a bracket perhaps... Look around for where there are two hoses running near each other that might benefit from a retainer then look for a stud that would match the nut.