There is a 360 - degree rotating stainless steel ball present for adjusting the angle of the holder and blue indicator lights for showing the charging status. (indabaa.com)
the fluid cranking system comes with 5 sealed stainless steel ball bearings and an instant anti-reverse bearing. (geekwrapped.com)
You can find these 5 ml amber glass roller bottles with stainless steel balls on amazon and on Rivertree Life. (usingeossafely.com)