To further muddy the water in this little puddle, there's also a "half and half" donut with a flat side for a rigid exhaust pipe flange, and a bevel for the manifold. One of the three designs will solve just about any manifold/pipe sealing situation.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!