The May 16, 1988 Chicago Tribune article "Cities Strike Back At Closings" offers a bit more detail on the move to pull the company out of Duluth:

Communities angered by plant shutdowns are starting to take bold legal steps that could significantly raise the cost of corporate decisions to close facilities.

While Congress and President Reagan continued to lock horns last week over workers' need for advance notice of shutdowns, lawyers for the City of Duluth, Minn., were preparing final arguments in a suit against Triangle Corp., based in Stamford, Conn.

The suit could establish a major precedent for communities fighting plant closings.

Duluth, which sold $10 million of tax-exempt industrial revenue bonds to help Triangle buy the locally owned Diamond Tool & Horseshoe Co. in 1981, alleges the hand tool manufacturer is violating the terms of that agreement by moving machinery to another plant out of state, costing Minnesotans jobs.

The city in February won a temporary restraining order in U.S. District Court in Duluth halting further movement of machinery. Final arguments in the case are scheduled for May 27.

"All we're saying is bring back the equipment and use it for the original purpose for which it was purchased and financed," said David Sebok, director of planning and development for Duluth. "They're not living up to their end of the (1981 bond) agreement."

According to local newspaper accounts, the city in late March introduced evidence of a secret plan to move production from Duluth to Triangle's other toolmaking plant in Orangeburg, S.C. Employment at the Duluth plant has dropped to 320 from more than 700 in 1981.

The plant's union, concerned about the job bloodletting that has affected its members, has joined in the lawsuit, said Tom Stillman, president of Direct Affiliated Local Union 18650.

Triangle officials refused to comment on the specifics of the case. However, Vice President Don R. Gifford did say, "We don't intend to close the plant, and we've told them that many times."

So far the response on Facebook has been all over the place.

Robert Larson says 1982: "They are protesting. The company that bought Diamond Tools was in the process of moving the company to South Carolina."

Elizabeth Smieja thinks early 1990s: "I remember this, my dad worked for the company and I remember this was when they were shutting down. I want to say early 1990s - like 1994."

Tracey Ellingsen agrees with Smieja: "My dad worked here. We're trying to pinpoint an exact date, but it was spring or summer of 1994."

Heather Lowe Williams wrote: "From the casual shirt and pocket object I’d say 1960s?"

Michael Valentine writes simply "1965."

Six years after posting this photo I'm provoked by a Duluth News Tribune "Bygones" item to lean in the direction of our mystery photo being from 1984.

News Tribune & Herald, April 17, 1984

About 400 striking workers at Diamond Tool and Horseshoe Co. in Duluth rallied outside the plant as they began the second week of their walkout over stalled contract negotiations.