-Bones 100’s Formula is an evolution of the white, MDI urethane we pioneered in 1977. This family of urethanes has grown to become an industry standard, and because we develop our own formulas in-house, we have been able to keep the Bones 100 formula continuously ahead of all other MDI based wheels in rebound and abrasion. This provides skaters with the very highest in performance at a price point that makes them a real value. “100” formula is a Bones exclusive. -Formula: BONES Original -Hardness: 100A -BONES Wheels; revolutionizing quality urethanes that help revolutionize the future of skateboarding.