The powerblock u90 stage 2 add on kit is part of the urethane series and is designed to replace 28 pairs of dumbbells or 1163kg 2564lbs of free weights it requires u90 stage 1 and is further expandable with the u 90 stage 3 kit together with stage 1 the kit offers a weight range of 2 41kg 44 904 lbs per hand