Special self locking oil pan bolts that use a smaller-than-standard hex head for tight spaces. Because of the hex flange head design, it will not fall back into the socket wrench, allowing for easier installation. Special under head serrations prevent loosening and the wide flange head distributes uniform clamping pressure for an better gasket seal. Includes two 1/4 inch-20 x 1/2 inch and (20) 5/16 inch-18 x 3/4 inch zinc plated, grade 5 bolts.