He’s used plastic zip ties, bamboo sticks and even cat food cans to open the locks dangling from gym lockers and storage sheds across the US.

Bill Johnson is now attracting a global following thanks to his YouTube campaign against Master Lock — offering a veritable how-to on ways to open its padlocks without a key.

“Stay away from Master Lock,” Johnson warns as his online alter ego, Bosnian Bill, in a November video, after opening one of the company’s locks in a few seconds by simply tapping on it with a small brass hammer.

The problem, he told The Post, is that the guts of many Master locks are the same.

“They have a wide variety of locks with different styles of bodies and shackles, but all have the identical junky core,” he said.

The former Army officer, who served 28 years on a bomb disposal team, calls up lock manufacturers to point out weaknesses in their products — and many of the smaller companies actually listen and improve their locks, he says.

“Master Lock, not so much,” said Johnson, 56, who hails from Fairfax County, Virginia.

“You get what you pay for,” he warned, conceding that some of the company’s higher-end locks work well.

Johnson said his war with Master Lock has even earned him angry letters from the company, which he said threatened to take legal action after he released a spoof video in which he pops open one of the company’s locks with a squirt of ketchup.

“There were threats after I made a silly video,” he chuckled. “I was just making fun.”

Johnson said he got into the lock game about a decade ago — after his bike was stolen.

He made his first YouTube video about five years ago while holed up in a hotel room in Ecuador, and has since amassed more than 170,000 devoted followers.

“I can’t believe it,” Johnson said. “I never would’ve dreamed that that many people would subscribe. I still don’t believe it.”

Showing Internet users how to pick locks could actually be aiding criminals, he conceded, but he claimed that most thieves don’t have the patience — or the time — to pick locks under stress.

And besides, lock pickers, he said, follow a code of honor.

First rule: All locks that are still in use are off limits, and second, hobbyists can only open locks that belong to them or that they’ve been given permission to use.

Johnson, who receives at least a couple hundred emails a day from fans, doesn’t answer suspicious questions either.

In one case, a college student asked him how to pick the lock on his dorm door.

“He wanted to know a quick bypass to get through doors,” Johnson said, adding that the user was banned from his channel.

For Johnson, lockpicking is part public service, part mechanical puzzle.

“It’s a manual form of Sudoku, but it’s useful,” he explained. “There’s always going to be a challenge.”

Master Lock told The Post it recognizes there’s an online community “who attempt to challenge the integrity of various brands of security products for fun and sport within their own controlled environments.”

“Master Lock offers an extensive range of security products, from basic levels of deterrence and protection up to maximum security. Consumers should choose a level of security based on their needs,” a spokeswoman continued.

“No one takes security more seriously than Master Lock,” she added, noting that the company has no record of threatening legal action against Johnson. “We are always innovating to further enhance the security our products provide.”