What the convention boils down to
A hook carries a number, and the number describes its size — roughly, the gape between point and shank. The scale runs downward as the number rises: a size 12 is small, a size 8 larger, a size 4 larger still, up to size 1.
Past size 1 the scale reverses and counts in aughts: 1/0, 2/0, 3/0, 4/0 and upward, each larger than the last. The corpus uses both halves — « #10/#8/#6/#4/#2 » in a hundred-piece assortment, « 3/0 » and « 4/0 » on jig heads, « 2# 4# 6# 8# » on ready-tied carp rigs.
There is no published method behind any of it. No body defines the gape, the wire diameter or the point of measurement for a given number.
What it does not promise
It does not promise agreement between makers. Two size 6 hooks from two houses are two different hooks, and the difference is not published anywhere.
It has nothing to say about the wire, which is what decides whether a hook opens under load. The trade names it in words, and most listings in this corpus name it not at all.
It has nothing to say about the pattern — circle, offset, octopus, dropshot — which changes what the hook does far more than one size step does. The corpus names patterns in titles, and those names are not sizes.
And it says nothing about the point, which is the part that actually fails first.
Where it shows up on this site
On the hook shelf, where the assortment boxes are sold by the range of sizes they cover. On the jig head shelf, where the size must be read against the length of the soft body rather than against the weight. On the carp rig shelf, where a ready-tied rig states its size and its hooklink together. And on the tied-hook sub-shelf, where the size arrives bound to a stated line diameter — and that pairing is the one a beginner gets wrong.
How it is read here
A page prints the size as the maker printed it, with the hash or the aught as published, and says what the listing states the hook is for. It does not convert between makers, and it does not tell anyone which size their fishing needs.
Where a listing gives a size with no pattern and no wire description, the page records both as unpublished. On a shelf where five hundred hooks cost twelve euros, that is the normal state of the information.
The questions that keep coming back
What size hook should I use?
The size is set by the bait or the lure body, not by the fish. A size 12 carries one maggot; a 4/0 suits a 12 cm soft body and will tear a 6 cm one apart. The pages print the size the maker printed and say what the listing states it is for.
Is a size 6 the same from two makers?
Not reliably. There is no published method behind the scale, so each maker sets its own gape and wire for a given number. A size 6 from one brand and a size 6 from another can differ visibly, and everybody in the trade knows it.
What does 2/0 mean?
It is read « two aught », and it is bigger than 1/0, which is bigger than size 1. Above size 1 the scale reverses direction and counts upward in aughts. The corpus shows 2#, 4#, 6#, 8# on ready-tied rigs and 3/0 and 4/0 on jig heads.
Does the number describe the wire as well as the size?
No, and that is the second gap. Wire strength is described separately, when it is described at all — the trade uses words like strong or a multiplier rather than a gauge, and most listings in this corpus give neither.
Last reviewed 22 September 2026