Abstract: The invention is a singular or plurality of variable weight, thread-socketed dumbbell system comprising a one-piece dumbbell and a plurality of removable attachable insert weights. The one-piece dumbbell comprises a handle bar fixedly attached to a pair of end-weights at opposing ends of the handle bar. Each end-weight may have one (1) to three (3) axially-aligned, inwardly-opening, threaded sockets. Each insert weight may be a disc-shaped weight having a protruding, threaded member. The insert weights are capable of removable attaching to the socketed end-weights. The invention further includes a singular or plurality of variable weight, lock-socketed, dumbbell structures comprising a one-piece dumbbell and a plurality of insert weights.