The versatility of the power block urethane u90 stage 1 3 is due to the adder weights within the core handle of each dumbbell these are easily changed depending on the strength of the user and the exercise you are wanting to do these amazing dumbbells can be used in multiple ways and will add on weights and the different handles available they can be adapted for your personal use or training key features of the power block urethane u90 stage 1 3 the u 90 stage 1 3 replaces 34 pairs of dumbbe