The original idea for these plugs came from a fan and supporter, Charlie, who wanted something that could be worn for extended periods and that would react to the motions created by walking or clenching the butt. This is what came out of his feedback. I designed these with a pronounced flange to help keep them in even while you are in an upright and relaxed state. The anvil base curves up naturally to hug either side of your hole … whichever provides the movement you desire, it also makes a great handle too.