This competition designed gasket is for standard bore (4.250" to 4.370") usage on 1965-90 Mark IV Chevrolet Big Block with aluminum heads. It is a preflattened copper wire ring with permatorque/blue stripe coating. The nominal compressed thickness is .039", with compressed volume of 9.7cc. These are composition design gaskets. Technical Note: This gasket is for Mark IV engines only, (1) gasket per package.