(Bloomberg) — The trading industry can't find consensus on when to apply the U.S. stock market's brakes during times of turmoil.

On Thursday, the nation's three major exchange operators upgraded their rules to help prevent a repeat of the chaos seen on Aug. 24, 2015, when many securities suddenly sank. But a major sticking point remains, according to an official who spoke at an event hours after NYSE Group, Nasdaq and Bats Global Markets announced their changes.

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