Does anyone know what system of measurement is used in assigning hook sizes? The reason I'm asking is I'm stumped why a #4 hook of one variety is so vastly different than a #4 hook of another variety. I would have thought that the criteria that made something a specific size would be universal and constant with shape being the variable for different styles of hooks. Recently, in ordering a hook size I was familiar with but in a new style to me, I was astounded at the size of the hook when it arrived. My curiosity was stimulated enough to see if anyone out here knows the answer.