In addition to automatic adjustment of dumbbells, it is generally adjusted according to the size of dumbbell pieces.
The weights of dumbbell pieces are usually: 1KG, 1.25KG, 1.5KG, 2KG, 2.5KG, 3.75KG, 5KG, 7.5KG, 10KG, 20k.
The weight of barbell bars is usually divided into 40KG and 20KG.
If you want to know, go to the gym and browse everything.