If you’ve ever moved from single-handed rods to double-handed (Spey) rods, you’ve probably wondered why an AFTM #9 line for a Spey rod is so much heavier than an AFTM #9 line for a single-hander. On paper, they share the same number — but in reality, they are completely different animals. Here’s why the confusion exists and why grain weights are now the most accurate way to match rods and lines.
The Origins of AFTM — and Where It Falls Apart
The AFTM system (Association of Fishing Tackle Manufacturers) was introduced decades ago to standardize line weights. It measures the weight of the first 30 feet of fly line (excluding any level tip) and assigns a number — #4, #8, #9, etc. For single-handed rods, this works pretty well because most casts use roughly that amount of line in the air.
But here’s the key: the scale only works if everyone is using the same type of line and the same style of casting — and that’s no longer the case in modern double-handed fly fishing.
Why AFTM Fails for Spey and Modern Lines
Spey casting is a different world. Instead of aerializing 30 feet of line, you form a D-loop and water anchor, and the “casting portion” of the line can vary massively depending on the line design.
- A long-belly Spey line might have a head of 70 feet. The AFTM system only weighs the first 30 feet, so most of the head is ignored in the rating.
- A Skagit head, on the other hand, could be only 25 feet long, so the entire head counts toward the AFTM rating.
Both lines could be perfect for the same 14-foot rod, but if you went strictly by AFTM, they would appear to be completely different weights — even though they’re designed to cast on the same rod. That’s a huge flaw in the system.
This is why matching by grain weight works so much better: it accounts for the full “casting portion” of the line — whether that’s a 25-foot Skagit head or a 70-foot Spey head.
Grain Weights: The New Common Language
Grain weight takes the guesswork out. Every modern double-handed rod now lists a grain window (e.g., 520–580 grains), which tells you the weight of the head the rod was designed to cast. From there:
- Lower end of the range = faster stroke, smaller flies.
- Upper end = slower stroke, bigger flies, heavy tips.
This way, you’re matching the actual working mass of the line, not an outdated system that assumes everyone is casting 30 feet of line overhead.
The Key Takeaway
If you’re fishing single-hand rods, the AFTM scale still works fine. For double-handers, it’s time to embrace grain weights. Ignore the printed AFTM number on the box and check the grains instead. It’s the only way to ensure your rod loads properly — no matter if you’re fishing a 70-foot long belly or a compact Skagit head.
Getting Started: Our Recommended Kits
If you’re just starting out with Spey casting, we recommend the RIO Scandi VersiTip Kits. They include everything you need — a perfectly balanced head, tips for all situations, and a wallet for easy organization.
- For rods over 13ft → RIO Scandi VersiTip Kit
- For rods under 13ft → RIO Scandi Short VersiTip Kit
These kits make setup simple, whether you’re fishing delicate presentations or adding heavier tips for sinking work.
