We named this bit the 'Burr' -aptly, because it was called a cuticle bit by manufacturers- BUT its not designed for the cuticle on the nail plate, its intended for the Eponychium, the hard skin above the nail plate. This bit is a Fine to medium grit, small metal 'ball shaped', bit, approx 1.5mm wide, used for hard skin & Eponychium clean up, or removing loose cuticle thats been lifted from the nail plate, Coarser option available too (green). NOT for the natural nail. Refer to your e-file training or Russian manicure training for use. Due to the nature of the Burrs use & required cleaning of them the lifetime of them is about 3-5 months. 
For professional use only.