Primitives that clearlooks special cases:
buttons scale_trough scale_slider
scrollbar_trough scrollbar_stepper scrollbar_slider
entry spinbutton_down spinbutton_up
menubar menu menu_item
handle resize_grip checkbox radiobutton
Windows uses approximately 370 "parts" plus their individual states to draw various elements in the operating system.
QT have about 24 primitives used to draw their toolkit.