Are you sure that's the right bolt? 3/8 UNC and M10-1.25 look kind of the same but are not compatible.
Oil, serioiusly just adding some oil can work wonders.
A new bolt can help too. bolts are cheap.
Depends if you stripped the bolt or the nut.
I'd start with trying a new bolt.
You can use a tap and die kit if you figure out imperial vs metric and the thread size and bolt diameter 10-24, m10 1.25, ...