I bought a new printer, and unfortunately the left nut for the lead screw isn't tapped.

I have the Anet A8, I confirm the threads are Tr8x8(p2). This is explained as "Tr" for trapezoidal thread followed by the nominal diameter in mm. The digits after the "x" denotes the lead of the screw (how much does the nut advance per revolution). The value between the brackets "p2" denotes the pitch. This means that the screw has 8 (lead) / 2 (pitch) = 4 starts.