Question: what is the difference between im6 and im8 fishing rods?
Answer: the article says that IM6 is the general "norm" for a flexible, but slightly heavier rod. Go to an IM7 and the rod gets lighter and stiffer - and go to an IM8 and it's even lighter and stiffer. ... this is a multi-part article about graphite fly rods, but the info translates to all graphite rod blanks.