: Ton rating is the overal modulus of the graphite fiber. Basically just another label, marketing idea. I think ton ratings are what the manufacturers have went by for a long time. The IM ratings are for consumers, so they understand ratings easier.

Higher the ton or modulus, the denser the material. More sensitivity in higher ratings. Also easier to break rods in higher ratings.

IM-6 graphite = 30+ ton material (Standard Modulus)
IM-7 graphite = 35+ ton material (Intermediate Modulus)
IM-8 graphite = 40+ ton material (Inter-high Modulus)
IM-10 graphite = 54+ ton material (High Modulus) ----