Clarification on Power screw's specifications please

Hello, I have a power screw. According to the specifications, it is M8x1.25. Does that mean the effective diameter of the thread is 8 mm while the pitch is 1.25 mm? Is the screw radius just 4mm?

From the internet, it looks like the lead angle is atan(Lead/(pi*effective diameter of the thread)) or atan(number of threads*Pitch)/(pi*effective diameter of the thread).

Could you please let me know how to find the number of threads and the lead (m/rev)? What is the lead angle in this case? Thanks in advance.