Deep Groove: Deep groove type ceramic bearings.
(The bearing works more than 6 month with good maintaining)
Agular Contact: The best Rito Dental Angular Contact Ceramic Ball Bearings.
(The bearing is Less Noise, works about 12 months with good maintaining)
Germany Bearing: Germany Myonic Angular Contact Ceramic Ball Bearings.
( The bearing is more quiet and stable, works more than 12 months with good maintaining)