This is a mechanical ponytail holder that doesn't pull your hair and stays put all day. It is easy to snap on and easy to remove. It has an inner diameter of 4cm. If you have exceptionally voluminous hair, the larger version is available here
It is available in two incredibly durable colors of nylon. The Gray PA12 can be dyed with RIT or any other dye used to color nylon. The Black PA12 is a deep black and can't be dyed.
Accessories for the Hairring can be found here