Tine wheel spacer and the bushing (515184) are part of the tow-behind aerator tine wheel (546048).
Due to engineering standards, some parts are updated or changed and are assigned a new part number. Previous part number was 521814. This part is the direct replacement.
WARNING: This product can expose you to chemicals including Lead and lead compounds, which is known to the State of California to cause cancer and birth defects or other reproductive harm. For more information go to www.P65Warnings.ca.gov