How long for new hairs to "fatten" up?

This does not necessarily have to be about MPB (I seem to be suffering from TE and HOPEFULLY" in recovery).

When a new hair enters the anagen phase and pops out of the scalp it is thin. How long does that hair take to reach its maximum shaft diameter?

Do new hairs grow slower than terminal hairs. I have dermascope and my terminal hairs seem to grow about 1/2 inch a month or so but all these emerging hairs seem to grow about half that rate (thus far).