Ring/Donut, or encircling probes are made to fit various fastener head diameters. They are mainly used for subsurface crack detection with the fastener in place. They are available in both bridge and reflection configurations.

Advantages
Ideal for subsurface defects.
Inspection can be done with the fastener still in place.
Various sizes available.
Available with Powerlink™ technology.
Available with bridge or reflection configuration.