5/16-18 x 3/4" Carriage Bolts, Round Head, Square Neck, Stainless Steel 18-8, Full Thread, Plain Finish, Flat Point, Quantity 25 By Fastenere Thread Diameter 0.3125" Head Diameter 0.719" Head Height 0.176" Square Neck Height 0.187" / Square Neck Width 0.32" 18-8 Stainless Steel provides strength and offers good corrosion resistance in many environments.