Replacement muscle belt for FIT, PROII, PROIII and Air support jackets. [Fit, Pro II Size Chart]: S, M 39.4 inches (100 cm), L, LL 43.3 inches (110 cm), 3L 47.2 inches (120 cm), [PROIII Size Chart] S - M, L-3L 47.2 inches (100 cm), [Other] 51.2 inches (130 cm) is a special size. The muscle belt and belt tips are different from the PROIII and Air, but this belt can be used without any issues. Please consider sizing up if you are in doubt.