В каталоге так объясняется:
ML (MEDIUM LIGHT ROD LOAD) G.Loomis suggests advanced casters select lines with “ML” rating to achieve a slightly positive line to rod balance. This balance rewards casters who can “hit” the forward stroke and generate higher line speed.
M (MEDIUM OR MODERATE ROD LOAD) Select an “M” line rating for a comfortable moderate rod load under medium
to medium long casts. Excellent choice for intermediate to advanced casters.
MH (MEDIUM HEAVY ROD LOAD) Select a “MH” line rating for additional rod load at shorter distances. Excellent for novice casters, or casting with heavy flies at shorter distances. Also a good choice to create a customized
“Skagit style” shooting head.
H (HEAVY ROD LOAD) Not generally recommended unless customizing a line for Skagit style casting.