I couldn't take off the OEM bolt to replace it 
It holds the steering stem nut in place so that the tension doesn't change.I'm just curious what's underneath the nut. I'd rather take it out and plasti dip it than cover it.
It's the same.I know your post is quite old, but just wanted to share this photo I found on google of a '09 Ninja 250 and the stock nut seems to match the black triple tree on the 250 quite well. Has the color of the triple tree on the 300 changed in color from the 250? It looks the same to me.