Basic anatomy of a fish hook.

image from mustad.no

To make-out various designs of fish hooks, will require a little idea of the basic anatomy. Dimensions & lengths vary between hooks models to suit fish species, tackles, legal requirements & fishing conditions.

For instance, the shank of a worm hook will be much longer to hold a worm. 

In case fishermen broke their lines therefore leaving the fish hooks still attached, fish hooks commonly are made from Iron/steel/Stainless steel(modern) materials which may rust & detach from fish's mouth due to corrosion by the seawater. 

I came across an uncommon fish hook which was made from solid chromium if i ain't wrong. Chromium greatly increases strength to withstand tension.  

Here's a breakdown of each anatomical section:

Eye-

The rear end of the hook may be twisted or drilled to create a hole for passing the fishing line through during tying. Eye is a crucial feature for a secure connection with the line, preventing slippage on a well tied knot. Large hooks, may have the joints at the eyes welded. 

(spade end)

 Some hook models will have a spade-end instead of an eye. 

image from repelsharks.com

A spade end is flattened at the end, causing a larger surface area looking like a spade. More typically designed on small sized hooks/fly hooks for smaller sized fish, to reduce weight for easier mimicking of lifelike prey actions on flies & sabiki rigs. Firm & tightly snelled knot to prevent line slipping over the spade end.   

Shank-

Shank is the length between the eye & bend. It'll withstand some tension, while keeping away from the line & bend for allowing hook's point to reach further into fish's mouth. A shank will also be partially wrapped by the line, particularly in a snell knot. Shank is also important in holding onto bait. 

Bend- 

Between the shank & point, bend is another critical feature which grips onto the fish while withstanding most tension as a terminal tackle. Weak hooks frequently break/straighten at this region.    

A straightened hook is good as a straight needle, giving the fish an instant escape. Stronger hooks are heat treated & forged bilaterally (especially at bend) to add strengths. 

Notice the flat surface done from forging process. 

Mustad 7691S(Stainless Steel)

Point & Barb- 

Where the 'Fish-on' begins, here's the first contact which sticks into the fish mouth. Upon sticking in, the barb buries itself into the flesh/bones. Fish feels hurt, but the barb is vital to prevent losing your catch. it latches against the tissues, preventing the hook from slipping out. Barb-less hooks have been produced for fishermen who'll wish to released their catch minimally traumatized, or do not mind losing it during the fight. 

Gape- 

Length of distance between shank & point. Wider a fish's mouth, wider a gape for a least harmful hookup. No doubt a narrow gape, to pass through a smaller mouth. 

Size:

Every hook models are manufactured in a scale of ranging sizes. Fishermen choose according to the size of their targets or partly the capability of their tackles. 

Actual measurements however, differ greatly between models; although size numbers can be exact.  

Smaller ranges are numbered from largest being no.1, till as large a number indicating smaller ones as the number grows. 

Example: Size no. 3 will be larger than size no. 8

Anything bigger than no.1, falls under a different indication marked with ' /0' behind the numbering; strictly starting from 1/0. The arrangement will go from small number being small size, to larger number being a larger size. Numbers hence grow as the sizes get larger.

Example: Size 2/0 is smaller than size 6/0    

In some large hooks models, manufacturer may not produce sizes below 1/0. 

Offset

What's a Kirbed hook? What's a Reversed? 

That's the either side which a hook's point is bent towards, at the bend. A reversed hook is bent towards it's left while facing you, whereas a kirbed hook is bent towards it's right. A straight hook well.... its pointed vertically. 

Reversed

image from mustad.no

Kirbed

image from mustad.no

An offset hook has a great advantage increasing hookups than a straight hook. A straight hook's point may miss it's contact upon a fish bite, whereas an offset hook is more likely to stick-in from another angle inside the fish mouth.