was visiting a friend on the weekend and the discussion turned to how to find absolute center on a 5/8" round aluminum bar , that I am making rad to firewall rods.
He simply grabbed a 5/8" socket, dropped a 3/8 punch with a point thru the end, then whacked it with a hammer. !!!!!!! The punch set runs from 1/8" up to 1/2" to cover all your 1/4----3/8---1/2" sockets holes.
voila , perfect center to drill down into and tap threads for spherical 5/16" rod ends left and right .
mike lynch