Maybe I am one of the few that was confused about all this talk about IM7, HM-60, and other ratings and what they mean for graphite rods.    All I knew was that I picked the rod for the info on it.  I would pick a rod with the medium action or medium fast or whatever. 

Recently, while reading an Ebook "Light tackle Fishing" produced by Craig DeFronzo,  http://micromunchtackle.com/  I came across the following information regarding the ratings of Graphite rods.  I hope it helps clear up other's  questions as it did mine.

Rich




Modulus, what does it all mean?
"Modulus is the degree of stiffness with which a rod rebounds from a bent position. This
term became important to the rod industry with the introduction of graphite. Various
companies strive for high modulus ratings with increased performance, casting and
sensitivity. Modulus is broken down into two categories I will speak of here:
IM graphite Intermediate Modulus
HM graphite High Modulus
This is a general rating of modulus graphite. It can vary slightly from company to
company but is mainly consistent.
Composite Graphite/Glass-roughly 25 to 30 million psi modulus
Intermediate 6-IM6-30 to 38 million modulus (38 is considered an HM for IM6)
Intermediate 7-IM7 about 35 to 42 million modulus
Intermediate 8-IM8 about 45 million psi modulus
This rounds out IM ratings

High Modulus HM-54- 54 million psi modulus
High Modulus HM-60- 60 million psi modulus
High Modulus HM-85- 85 million psi modulus
Graphite rod blanks are classified by their modulus ratings. This essentially describes the
parabolic action of the materials that the blanks are made of. Graphite is sorted by the
quality of fibers. The higher the modulus rating, the more sensitive, lighter and brittle a
rod blank can be.
There are several types of modulus material. The lower end materials are IM’s, which are
intermediate modulus graphite’s. These include composites which are combinations of
graphite and fiberglass and IM6 and IM7 graphite. Rods made with these materials can
be very good quality but they do lack many features that a higher modulus rod offers. IM
graphite is a bit more forgiving than HM materials. The highest rated rods such as HM-85
must be blended with reinforcing agents such as titanium or other materials to prevent
breakage. Generally the highest modulus blanks are mixed with other materials to prevent
rigidity and breaks. Some materials are titanium, kevlar, boron, and lesser graphite. As
you increase the modulus of a rod, you increase the price. You also increase the
performance: the sensitivity, and power are enhanced. However, the highest modulus
blank only becomes a true performer if the company that makes it designs a quality scrim
and rolls the rod correctly as well. There are companies who do not take the time they
should in producing rods and despite the use of high modulus graphite, their rods are no
better than rods built with IM graphite."

Reproduced with the consent of author Craig DeFronso @ Micro Munch Tackle

With a lot of other materials, the harder something is, the more brittle, but sensitive it can be. Harder materials transfer vibration better. That's why rod care is more important with higher modulus rods. Dings, nicks and scrapes can make them more susceptible to breakage. Food for thought.....