There is no standard for hook sizes. No ISO, no trade agreement, nothing. A size 4 from Mustad is not a size 4 from Gamakatsu. Hooked measures the hook you are actually holding — to a tenth of a millimetre, using any ordinary card as the reference.
Coming soon to the App Store and Google PlayThe problem
The makers are not even measuring the same thing. Some size on the gape, others on total length. Those are two different dimensions of the same object, and they do not track each other.
No ISO, no DIN, no agreement between makers. It simply never happened.
From 22 to 1 they get bigger, and from 1/0 to 10/0 they do too. Two series colliding in the middle.
On an eight-millimetre gape that is two whole sizes. Enough for your bait to stop sitting right.
How it works
That is not an approximation but a standard — ISO/IEC 7810, tolerance twelve hundredths of a millimetre — and it is the only measurement everybody carries. Note the word card: the format is fixed, the bank is not.
A library card, loyalty card or expired card — all exactly the same size. Flat on a table, shot from above. A coin works too.
From those follows a homography: the arithmetic that removes perspective. Shoot the card at an angle and that angle gets computed out rather than staying in the measurement. A loupe appears under your finger, because a finger covers exactly what you are trying to point at.
Shank, point, bend, wire. The gape is the perpendicular distance from the point to the axis of the shank — not the distance wherever it happens to land.
Gape, shank length, throat depth, total length and wire diameter. Below that: what that hook is called at every maker in the table.
Honesty as a feature
Most makers publish no millimetres at all. An app that still shows three decimals is pretending. Hooked puts a seal next to it instead.
Supplied by the maker themselves, from their own drawings.
Averaged from measurements by people using the app. The more measurements, the tighter it gets.
Read off published charts and catalogue images. Good enough to compare, not good enough to build on.
Today nearly everything sits at indicative. That is not a weakness of the app but the state of the trade — and it is exactly what we are asking the brands to change.
Inside the app
Ten chapters about hooks that nobody needed to know, and that everybody who fishes ends up wanting to. Checked, with the sources attached.
Two scales that meet in the middle and then run apart
One English market town made nine in ten of the world's hooks
The world's oldest hook is fourteen millimetres and fits in this app
Why this app exists, in one chapter
The circle hook asks you to unlearn what you were taught as a child
Another notation nobody explained and everybody needs
And four more: the alphabet of the point, every bend has a name, losing the barb, and crooked on purpose.
What it costs
That is not a trial and not a hook. The app is there to be used.
If your sizes appear in the app as indicative, that is because they have never been published. Send the real figures and it will say verified, with your name on it — to every angler who measures one of your hooks.
Privacy
Hooked works entirely on your phone. No account, no sign-up, no tracking. Photos are processed on the device and never leave it. Contribute a measurement to the brand tables and only the numbers travel — never the photo.
Rather not use a valid bank card as your reference. Not because the app does anything with it, but because that photo stays in your own gallery afterwards, number and all. Any other card is exactly the same size. If it has to be one: cover the middle, because only the four corners are measured.