Cast Iron Sign Base By SmartSign | 17&rdquo; Od Stand With 4&rsquo; Post And Sign Bolts & Nuts DURABLE. Sign base is made of solid cast iron and is sturdy enough to resist abuse such as bumps, dings or dents from vehicular impacts. Sign base is difficult to tip over, even in stormy weather with high winds, making it great for busy parking areas. INSTALLATION. 17" diameter base includes a post that inserts into the center of the base, 2 nuts and bolts and comes with predrilled holes for mounting signs. COMPATIBLE. Sign base is compatible with any sign measuring 24" x 24" or smaller. COMPLIANT. Sign bases are NCHRP 350 compliant, and approved for use nationwide.