What is the minimum pad size hole on the outer/inner layer?

FAQ about printed circuit boardsDESIGN RULES

This varies from manufacturer to manufacturer, but in general you can say that the majority of manufacturers can produce them as follows:
A = 0.15 mm
B = 0.20 mm
C = 0.30 mm

Illustrating pad size hole
For tighter constructions, please ask one of NCAB’s technicians for advice.