Regarding updated Adobe Sketch. Why why have the powers that be decided to downgrade the app by removing the finest line ie the 1.5? The finest line now is the 3. I discovered after much trial and error and experiment that the 1.5 thickness provided amazing subtlty and effects. Why have you done this Adobe???
In the current version there were changes made to the numbers displayed for brush size, but not to the allowed brush sizes.
In pre-4.0 versions of Sketch, the brush size was shown in points (2 pixels per point), so a 1.0-sized brush was drawing at 2 pixels wide. With v4.0 we moved to showing brush sizes in pixels, which effectively doubles all the brush sizes shown without actually changing the width.
The minimum pencil size used to be, in fact, 1.5 points, so now the same brush size shows as 3.0.
I hope that helps.