Safe lock groove lock groove helps you to adjust the weight you need, and prevent the dumbbell 

piece from falling easily save money & space 1 dumbbell equal to 7 different weight dumbbells,

you don't need to buy another 7 dumbbells and the compact design won't take you too much 

space high-strength plastic pedestal high density & strong toughness and keep the dumbbell 

piece not easy to fall easy to adjust quick change weight adjustments with push-pull design.