Bones bushings are like using milk in a milkshake instead of water. Well, sort of. Bottom line, they make your skateboard ride better. There is no break-in period. Just put them in, adjust and skate. Your trucks will be more responsive. Increased truck performance. Improves your skating experience. Your turns will be smooth and positive, not floppy or rigid. 3 Hardnesses: Hard Bushing: 96A, Medium Bushing: 91A, Soft Bushing: 81A