This kit replaces the original ball bearings. Reliability and rolling resistances is greatly increased by using the tapered rollers. Can be used with the original spacer [Have to fit with our shim kit] or without. These bearings FIT! We have been selling these for the last 43 years with no problems. This kit does both sides. We sell the correct bearings for this application. They are made by TIMKEN. Beware of cheaper kits, there are some people selling ones with either cheaper branded bearings or some are selling ones that are close to the right size but they are metric size. These are the correct size and are good bearings. We had a local guy using the metric "equivilant" and had a set go out each year. Ours lasted him over 10 years.