To mark the centerline, set a compass to span something more than half the width of the leg. Draw an arc from corner of the leg. The point where the arcs intersect will be on the centerline. With a centerline point on each end of the leg, place a scribe on the point, slide a straightedge up to touch the scribe. Do the same on the other end. When you have the straightedge positioned so that you can touch both points with the scribe, and in each case it is touching the straightedge - without moving the straightedge - scribe the line. Use scribes, rather than pencils or pens, because they make more precise marks.
Having done all this, I'm not sure I'd do it this way again. It might well be faster to layout the positions with compass and straightedge directly onto the top. Either way, you'll want to use a scribe rather than a pencil. Scribe lines are hard to see, and impossible to photograph, but the scribe and compass points click into them, allowing a precision that pencils simply cannot match.

The hacksaw will often damage the last thread when it cuts. Running a nut off the end will fix this. You'll have to run the nut all the way down from the other end. This doesn't take long, if you chuck up the rod in your drill and let it do the work. Hold the rod vertically, with the drill pointing down, and just hold on to the nut enough to keep it from spinning.
Post Woodworking’s Hampton shed is a major standout in design. The sleek farmers porch immediately draws the eye into its pure New England charm and provides the utility of shade and a cool place to sit and enjoy a cold one. Like all of our sheds, the six-panel doors which add to the structure’s aesthetic come standard. They’re made out of fiberglass to last through many decades out in the elements.