Diesel injector pump bolt??

[RustyOlRanger4x4]

Im 100% new to tinkering with diesels so excuse the probably dumb question. Can anyone identify this bolt/what it does? I know its something fuel related and im guessing some sort of bleeder screw? I cant find it on any of my parts manuals so maybe its not even suppose to be there? If I screw it in all the way the tractor doesn't seem to want to start but if I loosen it up much diesel spews out. Not knowing what it is/does my current idea is to either wrap it in Teflon tape and screw it in half way or find a matching size bolt and basically use it to lock the bolt to what its screwed into. And if it makes any difference this is on a Kubota B5100E 2 cylinder diesel. Any info is greatly appreciated!

 

[Fawken]

Looks like a pressure relief valve. Use a gauge to set it. It should send excess fuel back to the tank.

 

[RickB]

Should be a short bleed screw with a sealing washer that seals the head on the banjo bolt pictured. Someone replaced it with a bolt that is too long.

 

[Fawken]

Should be a short bleed screw with a sealing washer that seals the head on the banjo bolt pictured. Someone replaced it with a bolt that is too long.

Yep. Or what's left of a petcock valve?