The U.S. dollar index fell to a three-year low Wednesday and looks set for more declines after Treasury Secretary Steven Mnuchin said a weak dollar was good for U.S. trade.

The dollar index is now down 10 percent in the past year and broke below the key 90 level after Mnuchin’s remarks. According to Kensho, there are some big winners in the Dow when the dollar is falling.

CNBC’s analysis looked at when the dollar index is down 5 percent or more in a three-month period. That happened 29 times since January 1993.

The stock that did best on average while the dollar fell was Caterpillar, up 8.1 percent. 3M was the second-best performer, averaging a 5.3 percent gain, and Visa came in third, with a 5.2 percent gain.

Next was Apple with a 4.9 percent average gain, followed by Chevron, up an average 3.3 percent.

CNBC also studied which sectors do best during the same type of dollar decline and found the top sector was materials, up an average 3.9 percent, followed by energy, up 3.1 percent and industrials, up an average 1.9 percent.

A weaker dollar was not as positive for the S&P 500, which was up just an average 0.7 percent in the same periods.

Disclosure: CNBC’s parent company, NBCUniversal, is a minority holder of Kensho.