The AFFTA #Wt system

# Weight (wt)

Things you should know

It is a labelling system invented to help you get the right weight of line for your rod.

It was conceived in 1959, in the USA by the American Fishing Tackle Manufacturers Association (AFTMA), six years after the first synthetic line was invented (by Cortland). It was still the era of cane / wood and the earlier glass fibre rods. The advancement in rod technology and design since then has been huge.

The starting point is to assign a rating: “#wt” to each line and then to label rods as suitable for a given # wt. 

It sounds fine. It’s rather like relying on knowing what size your foot is to judge what size of shoe to buy… how many times do you try a shoe on and it’s not right?

It’s a good start but certainly not a perfect system.

So what actually is “#wt”? It is convenient short hand for the weight of the first 30 feet (exactly and only the first 30 feet) of the fly line, excluding the tip section before the taper starts. It was (and mostly still is) weighed in Grains (not grams). A Grain is an ancient measure of weight which dates back to the Bronze Age. There are roughly 15.4 grains in a gram.

Below is a graph of the #wt scale. Interestingly, you will see, it is neither straight nor does it start at zero.

Rods were and sometimes still are assessed by casting 30 feet of different lines. The line which casts best ( that’s to say : “fully loads the rod”) has its #wt assigned to the rod. 

So what issues does this raise?

There are too many to cover them all but a few well worth considering are these.

1. The rod may be more powerful than it’s rating would have you believe. Really…? Yes. Quite common. There are numbers which will tell you about this but not many people (even in posh shops) understand this. It’s called the Intrinsic Power of the rod and is the force required to fully load the rod. See table below and do google the “Common Cents System”

2. The line may not be what it seems. The 30 feet weight may be more than the #wt would imply. Do manufacturers really do that…? Yes. Quite common. So ask the supplier for the numbers.

3. You may do much of your casting at distances shorter or longer than 30feet when a different line weight might give better results. Very useful on smaller streams and big lakes.

4. Your rod may not suit your casting style. For example: If you have a fast rod but a leisurely casting style (or you’re a relative newcomer) : rod and line may be correctly rated but a heavier line will “slow the rod down” and make it a more comfortable, responsive cast.

5. Modern rods are very different (better?) than those made in the 1960’s. Lighter, stronger, much higher “modulus” of elasticity (so quicker). You can change line weights on the same rod to suit your casting conditions..

Points worth remembering:

The #wt system is a simplistic GUIDELINE, certainly not a rule.

You will not damage your rod by using a line that does not match the #wt on the rod. You may well have done this already without even knowing it. If the rod fails it’s a faulty rod.

#wt is sometimes referred to as “Grain weight”. Do not confuse Grains and grams (to easily done).

People love matching rod and line #wt … don’t be seduced by this… live a little.

This table joins up all the numbers: Rods on left, lines on right, common #wt rating in the middle and uses Dr William Hanneman equation as in the “Common Cents” system.

Also, please read this excellent article on the Sexy loops web site, which says it all, a slightly different way, extremely well.