Inside Bikes Not Bombs' Jamaica Plain facility on a recent Wednesday, dozens of volunteers dismantling bikes seem like old pros. Outside, Eleanor Millman, 25, instructs a batch of new volunteers how to separate old bike tires.

Millman, Bikes Not Bombs’ volunteer coordinator, started volunteering at the nonprofit that sends bicycles to Africa, the Caribbean and Central America a few months ago.

“I had some embarrassing moments when I’m like, ‘This is a pedal wrench — look, it’s long and thin.’ And the guy is like, ‘Yeah, I’m a bike mechanic. I know that,’” Millman said. “But I learned to ask, ‘Have you worked with bikes before?’ It reduces that embarrassment.”

About 30 volunteers gather each Wednesday at Bikes Not Bombs from 7 p.m. to 10 p.m. to prepare bikes for shipment and strip bikes for parts or recycling.

“The volunteers that come do a lot of the larger labor,” David Branigan of BNB said. “We’re only a staff of eight full-time people here, yet we are able to ship seven full containers with 500 bikes each per year to various projects overseas.

The way we’re able to do that is through volunteers.”

And the hard labor is rewarding for the volunteers in a way that other volunteering gigs don’t satisfy them.

“I’ve done other volunteering activities but you get a little bored once you know what you’re doing,” Millman said. “I made peanut and butter jelly sandwiches a bunch of times.

“There’s only so much technique to that whereas with this I’m learning more and more that I can apply elsewhere. And I’m also teaching other people, which is satisfying.”