Many fashion trends are a matter of inches. This one is a matter of cinches.

The firefighter jacket, a variation on the three- or four-pocket chore coat that features weighty metal clasps in place of buttons, has emerged as a curious, clangy spring jacket trend.

Adrien Brody, pre-Oscar win, wore a firefighter jacket in British GQ. Supreme, the streetwear agenda-setters, offers one in glossy cowhide for close to $1,000. Instagram-marketed brands like Ronning in Britain target early adopters with waist-length clasp jackets for about one third of that price. Vintage dealers, reporting increased interest, offer them for even less.

When worn, firefighter jackets are part fidget toy, part ASMR doodad. Those metal clasps lock together with a pleasing click, like a seatbelt on a roller coaster. As the owner of a vintage version from the nearly forgotten Italian label Energie, I can tell you that those closures are pleasing to idly toggle.

(As is perhaps obvious, it’s those shiny clasps that lend the coat its name. Authentic firefighter’s jackets feature metal clips that are easier to fasten than buttons or zippers while wearing gloves.)

Still, firefighter coats have been around well before the term ASMR was in use. A 1979 article in the St. Joseph Gazette in Missouri includes a photo of a man in a $150 metal-clasped “fireman’s jacket” from the defunct men’s label Hunter Haig. “Firemen take risks,” the accompanying article read. “That’s why they need a coat that can take the roughest treatment in the worst weather.” (Vintage dealers today will tell you to never buy a genuine used firefighter’s jacket, which may have, if not carcinogens soaked into it, then at least a smoky odor.)

Through the 1990s, jackets with gleaming clasps were common at mainstream-leaning labels: Liz Claiborne, Isaac Mizrahi and Structure, all of which are, if not shuttered, then shells of their former selves. It was Ralph Lauren, though, who was most closely associated with the style. Liam Gallagher, the Oasis front man, was wearing a color-blocked version from the brand back in 1994.

“Ralph definitely made them way more wearable,” said Matt Roberge, a vintage seller in Vancouver, British Columbia, who sells a $350 denim firefighter’s jacket with a corduroy collar and a $250 washed-out-to-near-pale-blue model, both from Polo, both decades old.

“I found a fireman’s jacket in a vintage store a few years ago, and I wanted to update it,” said Sigurd Bank, the founder of Mfpen, the Scandinavian label that produced the tri-clasp jacket Brody wore in British GQ. Mfpen’s version came in a washed denim fabric, with corduroy panels on the back. For the clasps, Bank used an Italian manufacturer who made closures for authentic firefighter outfits.

If the firefighter’s jacket is becoming popular, it’s doing so in the wake of a broader trend: the embrace of barn coats. Barbour and J. Crew have collaborated on a barn jacket, now nearly sold out. The GQs and Vogues of the world are hailing them as the coat of the moment. And designer labels like the Row and Auralee have brought the barn to the boutique with four-figure upsells.

“It goes no deeper than ‘I like these clasps,’ ” said Kiyana Salkeld, a product designer in New York who owns a pair of firefighter coats from Brut, a French label riffing on vintage workwear.