The strength of a hook is often designated by the 2X, 3X, 4X, etc. icon. This is to tell us the thickness of the wire used when producing the hook, which can make a big difference on strength of a hook. When a hook is named as 2X, it means that the wire is the thickness of the wire of the size larger. For example, a 2X strong hook in size 1/0 uses the size wire that is used on a standard hook in size 2/0.