M8 Flat head: Black finish Flat Socket head cap screw M8x 1.25 pitch, uses M5 allen wrench to tighten/loosen. The nut size is M8, which uses a 13mm wrench/socket to adjust. These bolts typically used on seats (upper and lower), seat struts, etc.
*To determine the length of a Flat head bolt, please measure the entire bolt including the head in millimeters