Rings AISI 440C stainless steel: 9Cr18 for inner ring and outer ringBalls: Si3N4 Ceramic balls or stainless steel balls (Ceramic Dental Bearings available for each item number.) it is also named Hybrid ceramic ball bearing, hybrid ceramic dental bearing, hybrid ceramic high speed bearing, hybrid ceramic super precision bearing, hybrid ceramic miniature bearing.Cages: polyimide, Torlon 4301 PAI, /stainless steel / PEEK, Phenolic, for cages, ball retainers, separatorsGrooved: SteppedSmooth: PlainCageless: Full complement design, Full Complement Bearings, (Full balls Surgical dental bearings)P5: Precision Grade: ABEC 5, ABEC 5P;P4: Precision Grade: ABEC 7, ABEC 7P; used for high speed dental handpieceHS: High Speed dental bearing, 350-400,000 RPM;LS: Low Speed, 50,000 RPMA/C: Angular Contact Ball BearingsK1 Inner Ring Separately, Angular Contact Radial BearingK2 Outer Ring Separately, Angular Contact Radial BearingD/G Deep Groove Ball Bearings, Radial Bearings