Not necessarily. The key to a good flange is to seal at the exhaust port locations. Hooker flanges are machined (using a milling process) to a surface flatness of + or - .0025 between the bolt holes. This process guarantees a proper seal at the port locations virtually eliminating flange leaks. Other header manufacturers simply run their flanges over a belt sander or body grinder. Hooker flanges are 5/16” (except on some unique applications) which is heavy enough to keep the header integrity but is pliable enough to seal each exhaust port. This helps compensate for variables in the head surface. Overly thick flanges are not as pliable and tend to have leaks. Hooker flanges seal the first time every time.