Why the numbers run backwards
Fly-hook sizes get smaller as the number gets larger. A size 6 hook is large; a size 20 hook is tiny. The scale steps in even numbers for most freshwater work — 6, 8, 10, 12, 14 — so a beginner rarely needs the odd sizes.
Gape, shank and wire
Two hooks can share a size number and still behave differently:
- Gape is the gap between point and shank. A wider gape hooks fish more reliably but can look bulky on a delicate dry fly.
- Shank length changes the body length. A long-shank hook suits streamers; a short-shank suits compact nymphs and emergers.
- Wire weight matters for floating versus sinking flies. Heavy wire helps a nymph sink; fine wire helps a dry fly sit on the surface film.
A working reference table
| Size | Hook type | Common freshwater pattern |
|---|---|---|
| 6 | Long shank | Woolly Bugger, leech streamers |
| 10 | Standard / heavy | Stonefly nymphs |
| 12 | Dry-fly | Elk Hair Caddis |
| 14–16 | Standard nymph | Pheasant Tail, Hare's Ear |
| 18–20 | Fine wire | Midges, small emergers |
Field note
When trout refuse a fly that looks right, dropping one or two hook sizes is often more effective than changing the pattern entirely.
Lead-free and barbless considerations
Some Canadian waters require barbless hooks or restrict lead. Many tyers pinch the barb with pliers before tying, and choose lead-free wire and tungsten beads for weight. Always confirm the rules for the specific water you plan to fish, as regulations vary by province and by individual river or lake.