Picture of the old Duquesne Brewery's Clock (shown with AT&T logo on face) located at Mary and 21st Streets in the South Side Flats neighborhood of Pittsburgh, Pennsylvania, on August 14, 2010. The clock was the largest single-face clock in the world when it was built in 1933. The former Duquesne Brewing Company building that the clock is on is from the 1950s, and the building behind it is the old Duquesne Brewery building from 1899.

The 60-by-60-foot (18 × 18 m) clock face, with a 35-foot (11 m) minute hand and a 25-foot (7.6 m) hour hand, both of laminated aluminum, is nearly twice the size of London's Big Ben, and was built in Georgia by Audichron for $12,500 and shipped to Pittsburgh. The clock, designed by Audichron founder John L. Franklin, is driven by a 1.25-horsepower (0.93 kW) Janett motor.

Originally located on Mount Washington, the clock's face was used as advertising for a succession of beverages, including Coca-Cola, and Ballantine, Carling, and Schlitz beers. By 1960, the Duquesne Brewing Company had bought the sign and installed it in its current location in the South Side. The Pittsburgh Brewing Company paid $44,000 to repair the clock when it took over in 1999, paying $5,000 a month to show its logo on the face. In 2002, Equitable Gas paid to have their name placed on the clock. In October 2009, AT&T took over the rights to advertise on the clock and has redesigned the face to display the traditional blue and white AT&T logo.