PCB Annular rings

What is an Annular Ring?

A copper ring attached to the surface of a pad around a connecting hole wall.

Drill size (Aperture) is the the size of the hole diameter.

An Annular Ring Width = (diameter of the pad - diameter of the hole) / 2

Normally Min width for Annular Ring is 0.15mm(6mil).

Drill Sizes (CNC): 0.2-6.3mm.(Min drill size is 0.2mm, max drill is 6.3mm. Any holes greater than 6.3mm or smaller than 0.3mm will be subject to extra charges)

Eg: 

1. R=0.12mm  H=0.2MM  D=0.44MM

The Annular Ring Width=(0.44-0.2)/2=0.12mm

2. R=0.15mm  H=0.3MM  D=0.6MM

The Annular Ring Width=(0.6-0.3)/2=0.15mm