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CHICAGO — It’s a tiny part that turns a Glock pistol into a mini-machine gun, capable of firing dozens of rounds within seconds.

It’s not only dangerous, it’s illegal, and as WGN Investigates has learned, people in Chicago are buying them online.

“I’m a little concerned that if it gets into the wrong hands there could be problems,” said Don Haworth, a retired U.S. Marine and local firearm expert.

But that may have already happened.

WGN Investigates has learned the ATF identified over 2,500 individuals nationwide who may have obtained the part, known as a switch, records show.

At least 118 people, possessing a total of 256 switches, fall within the ATF’s Chicago field division – an area that includes parts of neighboring Indiana and Wisconsin.

The ATF is now trying to apprehend the buyers and seize the illegally purchased switches.

The part is not exactly hard to find. In most cases, it was ordered online – from sellers outside the U.S., for as little as $30.

Often, the switch even sports a bogus “Glock” logo, to appear as if it’s made by the gun manufacturer, which it isn’t.

Cook County Sheriff’s police recently arrested two people accused of buying switches from China. Both are now facing felony gun charges.

Chicago police have confiscated more switches this year, compared to 2018.

But officials said they don’t know of a shooting where one was used, though that’s the fear.

“All it could do is just harm more and more people,” Cook County Sheriff Tom Dart said.

A Glock spokeswoman didn’t return messages from WGN.