Since the thread is formed not cut, the height of the peaks means as much as the depths of the valley. The thread on a 2 mm spoke is nominally m2.3. but in real life if you can accurately measure with a micrometer, they will usually fall somewhere between 2.2 and 2.3.
I have a Hozan, but it has been dedicated to 13 gauge spokes for the last 10 years since I acquired a Morizumi to handle the 14 and 15 gauge. When I was using the Hozan more regularly, I was replacing the rolling heads every couple of years. Maybe yours is due.