Line Weight

During a phone conversation the other day a friend was inquiring how to build a shooting head for distance casting. As we discussed the issue I mentioned that he might find the AFTM table helpful. They measure the grain weight in the first 30 feet of fly line. The response I got was "say what?".
AFTM stands for the Association of Fishing Tackle Manufacturers and you will find the AFTM number -- for example # 4 line -- directly above the handle. Heavier lines carry larger AFTM numbers. The manufacturers weigh the first 10 yards excluding the level tip and rate the line according to the table.


AFTM Table

AFTM number

In grains (range)

In grams

In ounces

3

100 +/- 6

6.48

0.228

4

120 +/- 6

7.78

0.274

5

140 +/- 6

9.07

0.32

6

160 +/- 8

10.42

0.366

7

185 +/- 8

11.99

0.422

8

210 +/- 8

13.61

0.48

9

240 +/- 10

15.55

0.55

10

280 +/- 10

18.14

0.64

11

330 +/- 12

21.38

0.75

12

380 +/- 12

24.62

0.86

 
One area that becomes problematic concerns the tip section which in many cases can be up to 2-feet in length.

Today's rods will handle weight above and below the specific AFTM number. However, placing a line several sizes above or below on the rod will over- or under- load it. To some extent under-loading can be compensated for by aerialising more line outside the rod tip. For example, if you were casting a 6-weight rod with a 4-weight line you would need 10 additional feet of line in the air to properly flex the rod. The problem with this approach is aerodynamics of the line itself. Anyway, that' what AFTM is all about.