316L Surgical Steel Ball Circular Barbell also know as a Horseshoe.
 
Available in 1.2mm or 1.6mm gauge with 6 - 14mm internal diameter.
3mm balls on 1.2mm and 4mm balls on 1.6 x 8 & 10mm

The balls can be unscrewed at both ends to allow for fitting or to change the balls.

Circular Barbell jewellery is very versatile and can be worn in many piercings such as septum piercing, ears, lips, daith, and tragus.