The special Self Locking timing cover bolts, use a smaller-than-standard hex head is ideal for tight spaces. Because of the hex flange head design, it will not fall back into the socket wrench, allowing for easier installation. Special underhead serrations prevent loosening and the wide flange head distributes uniform clamping pressure for an Ultra gasket seal. Bolts are zinc plated, Grade 5. Application: Chevy Small and Big Block, 1/4"-20 x 1/2", 10 pcs.