Robert Swinney writes:

Not to worry re. the sharp V at the root. Grind a tiny radius on the V
point of your threading tool (theoretically 1/8 pitch) and that will
eliminate sharpness at the root.

1/8 pitch? Shouldn't the valleys be truncated by 1/4 P? 1/8 P is the
truncation of the peaks? That's how I understand _Machinery's Handbook_.