625zz, 626zz, 608zz are widely used for aluminium sliding window fittings. The following is the suggestion that how to select suitable bearings for your sliding window rollers.
Main material for sliding window roller bearing are iron and carbon steel, due to it lower cost compare with chrome steel. The bearing quality and life is mainly depend on the raw material and cage component. As economic, Iron material is largely used for window roller application. It has two types of cage: metal cage and plastic cage(nylon cage). Metal cage can last longer lifespan, and plastic cage is with little cheaper price.There are white non zinc plated shield and yellow zinc plated cage. Zinc plate shield is better for anti-rust. For long term considering, we suggest you adopt metal cage and zinc plated shield.
Carbon steel material bearing is little higher cost than Iron material bearing, but the quality is also better. According to carbon percentage different, it has low carbon(mild carbon) and high carbon two types.Mild carbon has one more quenching progress compare with iron material bearings, and little softer than high carbon, good toughness. High carbon is in higher hardness. According to different producing way, it has punching type and super grinding type. Punching type means not grind the inner race, sometimes it has burrs and bore diameter is 0.1mm bigger than standard size. Super grinding means grind the inner race, the bore diameter size is about 0.05mm difference compare with standard size. Please notice for high carbon bearing no matter punching type or super grinding type will grind the groove for fitting the balls, for smoothly movement.