Cl.12.9 DIN 6921 Non-Serrated Frame Bolts: This bolt features a integrated flange with no serrations under the head and, depending on the diameter and length, a partially threaded shank. Available with a black phosphate finish, sizes range from M6 ~ M16 diameters. [A non-indented head is recommended as it prevents grease and dirt from accumulating on the head while providing a higher quality finish and appearance.]