For generations, the lit face of the Duquesne brewery clock has loomed over Pittsburgh’s South Side and served as a signpost for those approaching the neighborhood from Oakland.

Typically, that massive clockface — 60 feet wide, the largest in the U.S. — has had one sponsor or another. And while the face behind those gigantic aluminum hands has been blank for several years, it’s now promoting another product: Iron City Beer, whose maker, Pittsburgh Brewing Company, will stage a ceremonial relighting Thursday, Aug. 21.

“It’s just an advertising opportunity, but in a very big way,” said Pittsburgh Brewing president Todd Zwicker. His company is leasing the clockface from the big timepiece’s owner and operator, South Side-based industrial contractor J. Poli, Inc.

AT&T sponsored the clock for much of the 2010s.

The 3,000-square-foot clock was built in 1933 to advertise Coca-Cola and was originally installed on the side of Mount Washington, above the P.J. McArdle Roadway. In 1961, Duquesne Brewing purchased it to install on its facility at 21st and Mary streets, where the clockface bore perhaps its most famous slogan, “Have a Duke!”

Arguably, it was at least Pittsburgh's second most famous clock, after Downtown's Kaufmann's clock.

The brewery closed in 1972, but it continued hosting advertisers including Stroh’s Beer, WTAE-TV, Equitable Gas and, most recently, AT&T, whose ad ran for much of the 2010s.

Pittsburgh Brewing itself was previously a sponsor, advertising for a few years starting in 1999.

The clock advertises Duquesne Beer in this undated photo.

The adjoining structure, meanwhile, was home to the Brew House Association, formerly an artists’ cooperative and now an apartment complex.

Pittsburgh Brewing is no stranger to landmark billboards, having recently leased the big space on Mount Washington visible from much of Downtown and the North Side. But like the big clock itself, it’s migrating to the South Side Flats.

“If you’re up on the Boulevard of the Allies, as you know, you can’t miss it,” said Zwicker. “But you really can’t miss it anywhere in Pittsburgh.”

The clockface is twice as large as that of London’s famous Big Ben. The hour and minute hands are 35 feet and 25 feet long, respectively, and weigh a combined 4,300 pounds.

Thursday’s lighting is an invitation-only event, but of course, you’ll be able to see it happen — invite or no. That’s kind of the point.