PROFORM Wedge-Locking Header Bolts ELIMINATE the need to constantly re-tighten collector bolts, and without the need for clips, pins, racing-wire, chemicals or gunk. The secret is in the Wedge-Locking Washer's super-hardened external teeth that "bite" into the bottom of the bolt head and the top flange surface. Vibrations that normally cause other bolts to loosen, are blocked by the wedge-locking action that uses tension, instead of friction to stay snug. In fact, contact with oil actually facilitates the effect. Installs/uninstalls with a normal wrench, lubricate, and then reuse. Each set comes with sixteen Hex Head, Grade 8 (12.9) steel bolts (3/8"-16 thread, 3/4" long) with a black oxide finish, and pre-assembled Wedge-Locking Washers.