Anyone Know What This Is?

on vehicles with air shocks, it was necessary to move the top of the rear shock away from the body mounting location because the top of the shock is fatter than stock, so this goes on the mount shaft between the rubber bushing and the body. Since this means that the shock mount stud does not have as many threads sticking out of the rubber bushing, there is a companion threaded piece on the outside of the bushing that replaces the stock conical washer and nut.