We sell primarily three types of rings:
Type T has teeth and looks like a cog wheel. It may in some cases also have a flange on one side.
Type W has windows (holes) instead of teeth.
Type M has a multi-pole magnetic strip on the exterior or on the side.
Type T and W are passive rings. When the wheels rotate, they create a small inductive voltage difference on the wire windings of a nearby magnetic sensor.
Type M are active rings as they have builtin alternating magnetic poles, which produce a magnetic fluctuation and generates a more precise Hall effect.
See our product catalog for further specifications and images.