Is there a way to obtain the size of the buttons/arrows of a Qt QSpinBox?

Note: This question has nothing to do with changing the style of a QSpinBox. On the contrary: The intent is to use the QSpinBox style as given and obtain at runtime the size of its buttons/arrows, which will be different for different platforms, for the purpose of fine tuning the layout constraints in which the QSpinBox is one component.

Also: The QStyle class does not appear to provide PixelMetric values for the button/arrows sizes.