sorry to be so technical in the title... 
Every time I started the boat the nut where the key goes in would loosen and the whole thing would turn so today I had the brilliant idea to tighten it
As you can see in the pic, I broke it while attempting to tighten it. It didn't take much to break it either
Questions are
1. what is that thing called?
2. How do I fix/replace it?
I'm hoping that by holding it with one hand I can still turn the key with the other because I'm going fishing in the morning
Thanks for any tips

Every time I started the boat the nut where the key goes in would loosen and the whole thing would turn so today I had the brilliant idea to tighten it
As you can see in the pic, I broke it while attempting to tighten it. It didn't take much to break it either
Questions are
1. what is that thing called?
2. How do I fix/replace it?
I'm hoping that by holding it with one hand I can still turn the key with the other because I'm going fishing in the morning
Thanks for any tips
