Why do some PCBs have these circular rings? Are they plated through hole vias?
This is a mounting hole for a screw. Smaller holes around - Vias are used to reinforce mounting point.
Copper ring around the hole together with plating increases stiffness of PCB. Vias around protect this ring from being peeled-off by screw head.
Another purpose of Vias might be to increase electrical or thermal conductivity between PCB layers and the screw.