Fly Fishing Hook Sizes Explained: How the Numbers Work

It is crucial when you are fishing to have the right size fly. Often hook size is more important than the pattern itself. If you can roughly imitate the color …

It is crucial when you are fishing to have the right size fly.

Often hook size is more important than the pattern itself. If you can roughly imitate the color and shape, you are in the ball game.

But unless your fly is close in size to the natural insect or prey item, it will often go ignored.

The numbering system for fly tying hooks can be confusing, so we’ve tried to break it down as simply as possible.

Fly Fishing Hook Size Numbering System Explained

We have broken this section down into freshwater and saltwater fishing as it makes a relatively clean delineation for ease of explanation.

Freshwater Fly Fishing Hook Size

  • The higher the number, the smaller the hook
  • Small hooks run from a size 32 (tiny) to a 2 (big enough to be used on streamers a few inches long). This chart from leading fly hook maker Tiemco shows the actual hook size of all its styles and types of hook if you print it in A4: 
  • The size of hooks is denoted with a # in front of the number and ascends as even numbers: #32, #30, #28 … up to #2.
  • For stream fishing for trout, you are usually fishing with flies in the #20 to #10 range
  • For streamer fishing, flies are usually in the #10 to #4 range
  • For salmon and steelhead, flies can be as large as #2 (although smaller flies right down to #12 can be used in certain circumstances)
  • Due to variations in the style of hook (dry fly, wet fly, streamer, etc.), there are no standard dimensions for, say, a #10 hook. Taking length as an example, this will depend if the hook is, for example, a long-shanked hook designed for a streamer or hopper pattern or an emerger hook, which will be significantly shorter. (For hook styles, check our companion on that topic).
  • Also, one manufacturer’s #10 streamer hook may not be exactly the same length as another’s.
  • Despite the lack of standardization in dimensions, you can be assured that within a given hook type/brand, a #10 will be one size bigger than a #12.

Saltwater Fly Fishing Hook Size

  • Saltwater fly hook sizes obey the same principles as freshwater in that the higher the number, the smaller the hook.
  • The key difference with saltwater fly fishing hooks is that they tend to be bigger, so we need to go beyond #2  .. the largest hooks on the freshwater scale.
  • Beyond #2, you move into the “aught” designation. With this system, there are three key things to know
    • We use a ‘/’ and a ‘0’ after the number. And we say a 3/0 hook is a “three oh” or “three aught” hook if we are saying it out loud.
    • Note the sizing order is reversed. A LARGER number indicates a LARGER hook. So after #2, you’d have 1/0, 2/0, 3/0, 4/0. 
    • We got up in intervals of 1 … so 1/0, 2/0, 3/0, etc.
  • Hooks range right up to a 20/0 but for fly tying purposes; we are really talking about sizes up to 5/0 

Parts of a Hook Explained

There are a wide variety of different hook types for targeting different species or imitating different insects, crustaceans, and fish … or any sort of fish food.

Hook Eye

The hook eye is the circular loop that you tie the line to. Hook eyes can be straight (in line with the shank), down eye (the eye dips by about 45%), and up eye. The selection of the eye type depends on how you want the fly to present relative to the line. The most commonly used eye configuration is down eye.

Hook Shank

The shank is the section of the hook that runs from the hook eye down to the start of the bend. Kind of like the backbone of the hook. The hook shank varies not only between sizes but between styles of hook.

While most hooks are straight shank, some hooks can also have curved shanks, such as those used in some caddis patterns and also certain nymphs.

Generally, for a standard fly hook, the length of the shanks is roughly two times the gape width. Shank sizes often vary depending on the type of hook (explanation in the section below).

Hook Gape

The gape (or gap) is the distance between the bend and point of the hook. The size of the gap determines the size of the hook.

Different patterns call for different gapes or gaps.

It is worth noting, hooks with wider gapes increase your chances of hook ups, although they offer more leverage for a powerful fish to open out your hook.

Hook Bend 

 The bend is the section of hook where it curls back on itself through about 180 degrees joining the shank and the point and barb.

There are a few different hook bend styles, including the Limerick bend, the Sproat bend, the York bend, Perfect Bend, Aberdeen Bend, the O’Shaughnessy bend, and the Round bend hooks. These described different curvatures. For basic trout flies, hooks have a round bend or sproat bend. It’s best not to get too hung on bends as this element is not as important as other parts of a hook.

Hook Point

Believe it or not, there are different types of point including straight edge and needle point. This is not something to obsess about for a trout hook, as your quarry has a soft mouth. For saltwater fly fishing, where many species have hard mouth parts, hook penetration can be a factor. The main thing here is to keep hook points as sharp as possible to maximize hook penetration.

Hook Barb

The barb is the little ridge that sticks out of the hook just below the point. The idea of the bard is to prevent the hook coming out. 

More and more fishermen and women are using barbless hooks now to avoid injuring the fish and allow for quick releases.

Hook Wire

Different hooks are made of different gauges (or thicknesses of wire), and they vary in weight and application. A dry fly hook – given it needs to float – will be made from thinner gauge wire than a nymph hook or a grubber hook, which needs to sink.

Fly Fishing Hook Properties Explained

Manufacturers use the ‘X’ system to explain how the properties of hooks vary across shank length, gape width, and wire gauge. Once again, this can be a bit tricky to the uninitiated but is easily grasped with a bit of explanation.

Take the Mustad C67S hook – a popular trout hook type for scuds, curved nymphs, and egg patterns.

This type of hook has the following qualities – 2x Heavy, 2x Short, 3x Wide, Straight Eye.

So what’s all that mean?

Basically, we are talking about how much it varies from the standard fly fishing hook size across these qualities.

Each number before the X denotes a step up or down in a particular quality – so 2x heavy means the wire gauge on a #14 Mustad C67S is equivalent to that of a #10 standard Mustad Hook (two steps up from the #14). 1x heavy would be wire equal to a #12 standard Mustad hook. 2x short means the shank length is equal to that of a #18 standard shank Mustad hook, and 3x wide means the hook gape (or hook gap) is the size of a #8 standard Mustad hook.

These qualities have the following variables:

  • Wire: Heavy/Fine
  • Shank: Long/Short
  • Hook gap or gape: Wide/Narrow

Final Thoughts on Fly Fishing Hook Size

Remember to use our fully searchable online hook store to find the right hooks for your fly tying.

We hope that this article and the accompanying video explanation will help to explain fly hook sizes in a simple way and cut through the complexity. After reading/watching, you should be able to select the right fly fishing hook size and type of hook with ease.

Fly Tying Hook Sizes Explained in This Accompanying Video

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Rick Wallace is a passionate angler and fly fisher whose work has appeared in fishing publications including FlyLife. He's appeared in fishing movies, founded a successful fishing site and spends every spare moment on the water. He's into kayak fishing, ultralight lure fishing and pretty much any other kind of fishing out there.
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