Seamlessly adapt between any spread bore manifold and square bore carburetor. Or the reverse.  This adapter is referenced in the Holley Avenger 2-BBL TBI Fuel Injection Kit's instructions.  While that kit includes both a 2-BBL TBI to square bore and 2-BBL TBI to spread bore adapter, at times using this 4-BBL square-to-spread bore adapter makes this work much more smoothly.