The bell-ended anal plug can be inserted to the depth of either of the two ridges. The linear design means that no matter how much or how little is inserted, you will feel the electro sensations coming from either side of the probe.

You can also use this bi-polar probe as a uni-polar probe by just connecting one cable instead of two. Stimulation will only be felt on one side but by adding a smear of conductive gel across the base will effectively create a fairly good uni-polar probe.