New ProForm set of header bolts for Pontiac engines using 3/8"-16 threaded holes. These are a wedge lock design (see photo #2), where the washer under the head has grooves and teeth to prevent the bolt from loosening.  Size is 3/8"-16 x .75" UHL.  These are 6-pt head black oxide steel.  Set of 12 bolts/washers.  Fits Pontiac engines with 3/8" holes.  Rule of thumb is you want 3/8" minimum thread engagement into the cylinder head.  Bolts that are too long will bottom out into the head and leak.  So you would measure your header flange and gasket and add 3/8" to determine the minimum length bolt you need.