An unknown number of guns are being built with the mechanisms, causing problems for the police and ATF officials. Photo: An ATF agent holds a generic unfinished receiver, back, and one that has been manufactured, front, at an ATF field office in Washington, on May 06, 2014. The ATF is trying to crack down on the trade in the makeshift guns by targeting shops and individuals who offer to turn the unfinished receivers into functional pieces for firearms. (Photo by Bill O'Leary/The Washington Post)

Front end detail of the Hyundai Santa Cruz crossover concept truck as it is displayed during the first press preview day of the North American International Auto Show in Detroit, Michigan January 12, 2015. (Photo by Rebecca Cook/Reuters)

Models pose alongside the Kia SP SUV Concept car after its launch at India Auto Show 2018 in Greater Noida, February 7, 2018. The biennial automobile exhibition opens to public Friday and runs till Feb. 14. (Photo by Saumya Khandelwal/Reuters)

A performer poses with “The Gronkle” and “Deadly Nadder” at the How to Train Your Dragon Media Call at Fox Studios on November 29, 2011 in Sydney, Australia. The “How to Train Your Dragon Arena Spectacular” world premiere will take place in Australia in March 2012. (Photo by Brendon Thorne/Getty Images)

An officer of the Afghan border police throws an assault rifle to a policeman participating in a military exercise on the outskirts of Herat, Afghanistan, Monday, September 7, 2015. Twelve female and seventy male border police personnel participated in the military exercise near the border with Iran in Herat province. (Photo by Hoshang Hashimi/AP Photo)

Germany, Business couple making love under desk. (Photo by Roman Maerzinger/Getty Images)

“The Personal Urban Mobility and Accessibility (PUMA) is an experimental electrically powered road vehicle created by Segway and adopted by General Motors as a concept vehicle representing the future of urban transportation. It operates on two wheels placed side-by-side, a layout that differs in placement from motorcycles which instead have their two wheels placed at the front and rear”. – Wikipedia

The Project P.U.M.A. (Personal Urban Mobility and Accessibility) prototype is displayed for the media April 7, 2009 in New York City. (Photo by Mario Tama/Getty Images)

Wales' Gemma Frizelle competes in the Team Final and Individual Qualification Sub Division 2 at the Coomera Indoor Sports Centre during day seven of the 2018 Commonwealth Games in the Gold Coast, Australia on April 11, 2018. (Photo by David Gray/Reuters)