Adj.brake pushrod issue

Gee, why not just the 1/2 to 9/16 and be done.
Maybe i didn't elaborate enough. Do not have 1/2" bolt only have 9/16. Would like to use same type bolt that has o ring ride right where the banjo is supposed to ride. I could buy a cheaper bolt that isn't just for brake pedal but there has to be a reason why there is an oring on bolt.