The Supreme Court on Friday overturned a Trump-era ban on bump stocks, ruling that the Bureau of Alcohol, Tobacco, Firearms and Explosives exceeded its authority by determining that the gun attachments turn firearms into machine guns.

The case was decided 6-3, with Justice Clarence Thomas writing the majority opinion and Justice Samuel Alito concurring. Justices Sonia Sotomayor, Elena Kagan and Ketanji Brown Jackson, the courts three liberals, dissented.

What are bump stocks?

Bump stocks are attachments for semiautomatic rifles to allow them to fire faster. It harnesses energy from the gun’s kickback to allow it to slide back and forth rapidly.

The stock “bumps” between the shooter’s shoulder and the trigger — hence the name — which allows the shooter to fire multiple, rapid shots while holding the trigger down, rather than pulling it multiple times.

A bump stock allows a semiautomatic rifle to fire at close to the same rate as a fully automatic machine gun, which civilians are not allowed to own.