The thicker wire of these swivel eyes makes for improved knot strength in comparison with other swivels of similar size.
Sizes 8 or 10 for general fishing - I use the 8s on my crankbait traces. Size 12 or 14 for ultralight or fly traces, or other rig applications. Size 5 is the jerkbaiter's perfect swivel. Also suitable for other heavy predator fishing situations.
Size 2 for continental catfish, Nile perch, or sturgeon hunter's dream swivel.