A fantastic replacement for multiple set of weights the powerblock u90 stage 2 add on kit b requires stage one and 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 its a practical way of improving your workout without incorporating multiple dumbbells and excess amount of weight to keep your body in shape and build up an impressive mass the powerblock set can be expanded