Stage 8 Locking Fasteners 8912A Double Hex Head Header Bolt Kits Steel. Condition is New. Shipped with Standard Shipping. This kit will work on a big block ford or big block Chevy. The bolts are 3/8"-16 1" long. tighten the bolt to spec, place the locking tab around the head and against the header pipe, install the C-clip and the bolts can not loosen.