Firearm part, in one of the earlier amendments, is defined as barrels for firearms and “a slide for a handgun”. I got that wrong before. Those would be the parts that a person would need a licence to purchase. The intent behind the legislation is that these two parts are the most common to create a 3-D or illegally manufactured firearm and the hardest to make.
On May 10th, 2023. See this statement in context.