progressThickness

The progress bar's one dimension: a dot is Width="4" Height="4" and both rectangles of the determinate track are Height="4", so it is a single number in three places.

Here rather than beside the component because it has to move with scaled. Left as a constant it stayed at 3 dp while every other measurement on the page grew, and a scaled-up theme got a row of specks — which is what it looked like.