Do you mean a round rod with a flattened ends w/ bolt holes? This is a rear fender brace, right?
I'll tell you what I did when I forgot which hole my rear braces bolted to. I hung the fenders, then crawled under it and loosely bolted the rod to the lip of the fender. This gave me the endpoint for one side, I just pushed the flat end of the rod against the frame and looked for a hole that matched.
