Hook sizes:

[AndyS]

Hook sizes are not the same from one manufacturer to another. Size measurements relate to the width of the gap, but each manufacturer uses its own scale, and although some hooks are quite similar in size, they are not identical, so size designation is relative to individual manufacturers and specific patterns.

[italianfisherman]

that is true... u will look at one 3/0 & look at another 3/0, & u will see a diff... (gamsu/owner)

[Ryan W]

AndyS is right on the money. Best thing to do is to take a look at the hooks you plan to buy beforehand. If you fish a lot, you will know which are the size you are looking for (mustad 2/0 vs gammie 2/0, ect), and can order them online or whatever in order to get a discount and not have to go anywere to pick them up.

[bigfishtale]

Owner SSW hooks tend to run a size smaller than a comparable Gami Octopus hook. Owner 4/0 looks like a Gami Oct 3/0 IMHO.

[italianfisherman]

Owner SSW hooks tend to run a size smaller than a comparable Gami Octopus hook. Owner 4/0 looks like a Gami Oct 3/0 IMHO.
I'LL 2ND THAT...

[The Sinker Man]

There is also a difference in sizes, but different styles from the same manufacture..