Shape
Four rounded-rectangle steps, with radius tracking height. That correspondence matters more than any individual number.
6
24px controls
8
28 / 32px
10
40px
12
Cards / dialogs / overlays
The one pill exception
A 40px control with a 6px radius looks unfinished; the same control at 20px looks like a different product. Primary controls are never pills — even the largest button caps at 10px. full is reserved for things that are genuinely circular: status dots, the slider knob, the switch knob. The switch track is the one pill exception, and it earns it: a rounded-rectangle switch reads as a checkbox.
Radius is the only shape device. No bevels, no notches, no decorative borders, no gradient strokes.