688 bearings is a kind of deep groove ball bearings.
688 bearing parameters
As to 688 bearing, the number 6 of the bearings represent deep groove ball bearings, the middle number 8 represents the size series, and the number 8 represents the inner diameter of 8 mm.
688 bearing can be divided into the closed style and open style,there is no cover on both sides of the open style bearing,which indicated by 688 directly; with a lid, the lid has dust cover (688ZZ) and rubber seal (688-2RS).
With dustproof cover 688 ZZ bearing have dust-proof function, high temperature resistant capability; and the rubber sealing cover 688-2RS have waterproof and dustproof function, the sealing and heat dissipation capability is poor, not suitable for use in high temperature environment, but under the same conditions ,it’s low noise compared with dust cover.
688 old type is 618/8, the dimension is 8mm*16mm*5mm, with regards to non-standard bearings depends on the actual size and dimensions, but the size is not too much different, the actual use of non-standard bearings is relatively small and the cost is high.
The materials of 688 bearing are carbon steel, bearing steel (GCr15), stainless steel (440 or 304), ceramic ball, plastic, etc., the cage material is carbon steel, J steel stamping, nylon cage and so on!
688 bearing applications
688 bearings has a wide range of uses, such as massage belts, electric toys, electronic parts, instruments and meters, sports equipment, pulleys and so on.