A fantastic replacement for multiple set of weights, the Power Block U90 Stage 2 Add on Kit B requires stage one & two A for a complete set to work with. Change your old dumbbells for a functional, space-saving alternative which delivers the same amount of weight as 28 pair of weights. It's a practical way of improving your workout, without incorporating multiple dumbbells & excess amount of weight to keep your body in shape & build up an impressive mass. The powerblock set can be expanded to a next level if you need additional bulk, & it comes with a lifetime warranty if used in home environment.