McMaster-Carr has 18" eye bolts in several shank sizes: https://www.mcmaster.com/products/screws/shank-length~18/ these are galvanized. be careful, with the plating thickness one must use the supplied nut. If this is to hold the equilizer plate, the 5/8" listed capacity of 3500# might be on the light side depending on your install? greg/na8v