Permanent concrete monuments shall be accurately set and established at the intersection of all outside boundary lines of the subdivision; at the intersection of those boundary lines with all street lines; at the beginning and end of all curves; at points on curves where direction changes; and at such other points as are necessary to establish definitely all lines of the plat; or as provided for in the Ohio Revised Code. Stone or concrete monuments shall be at least six inches in diameter and shall be provided with an appropriate center point. Solid iron pins at least three quarter inch in diameter and at least thirty inches long may be used at all other points.