Black or silver, it was shaped like a camel back trunk, with two chrome latches on the front. A swing arm locked the glass-lined thermos inside the domed lid. The metal “workingman’s” lunchboxalthough plenty of women carried one, toosymbolized the can-do spirit of manual labor.

My dad carried a black metal lunchbox to Delco-Remy Plant No. 1, a General Motors factory in Anderson, Ind., where he worked the night shift as a machinist. Each weekday afternoon at around 3:30, my mother would lovingly stuff his lunchbox with enough food to feed the Donner Party: five sandwiches on white bread (she eventually switched to wheat)two grape jelly, plus one each of bologna, pickle-pimento loaf and peanut butterplus an apple and a thermos of whole milk.

The work was such that my father did not get fat. At 5 feet 10 inches and 185 pounds, he had forearms the size of rear axles, sculpted by years of wrestling with borers and grinders, jig mills and lathes. He would stand all night at his workbench, his feet snug and sweating in leather steel-toed boots that deflected sharp flakes of hot steel onto the oily concrete floor.

Meanwhile, in the cool cave of his lunchbox slept the sandwiches, which, like his toes, needed protecting.

In the late 1800s, workers carried their lunch in metal pails or tobacco tins. Around that time, British scientist James Dewar invented the vacuum flask, according to the Thermos company website, and two German glassblowers began manufacturing it in 1904. A contest was held to name the invention, and a Munich resident suggested Thermos from the Greek word “Therme,” meaning heat. In 1925, George F. Walter and John M. Hothersall improved upon the lunchbox’s design and functionality by lodging the thermos inside the domed lid. The purpose was to provide, the patent stated, “a bottle holder of the simplest and least expensive form consistent with efficiency and serviceability.”

When U.S. manufacturing peaked in 1979, nearly 20 million men and women were working in factories and mills. A sturdy metal lunchbox could withstand the rigors of the harsh environmentsheat, cold, falls from tables and benches.

Yet as the number of blue-collar workers declinedfrom 1980 to 2005, the U.S. lost 4.5 million manufacturing jobsso did the need for the metal workingman’s lunchbox. My dad got a promotion and began wearing a tie and regular shoes to work. He carried his lunch in a plain brown sack.

The 21st-century American labor market has transformed from factory work to predominantly service or desk jobs. To bring a metal workingman’s lunchbox into a white-collar workplace would be pretentious. What would we protect our lunch from? Falling kilobytes? Paper cuts? Office gossip?

Business people go out for lunch and expense it. Fast-food employees eat the free meal that comes with the joba sandwich, chips or fries, and a drink. Journalists, web designers and software engineers order takeout or hit the drive-through and wolf down their meals at their desks, coating their computer keyboards in crumbs and condiments.

Some people still brown-bag it, but the standard-size sack can’t accommodate a plastic tub filled with last night’s lasagna or a frozen box of Weight Watchers meatloaf with mashed potatoes.

Today’s lunch duffles are fashioned from recycled plastic or soft-side vinyl. They are insulated, cushy. Our lunches no longer need to be protected; they want to be coddled.

In the daily ritual of lunch making, my mother’s final touch was to write my father a note and then slip it among the sandwiches. I don’t know the contents of these lettersto read them would have been an unthinkable breach of my parents’ intimacybut I always knew when she had finished one by the brisk strokes of her pen as she dashed a constellation of x’s and o’s at the bottom of the page.

My father took his lunch break at 8:30 each evening. I imagine him sitting at his workbench with his lunchbox agape and reading a love letter from his wife, who at that moment was readying their children for bed. Then he would neatly fold it and place it inside for safekeeping.