Convertible circular needles are a fantastic invention. Why should you need to own each size and length of circular needles when you can just swap tips? I have fallen in love with the Options Interchangeable Harmony Wood Circular Knitting Needle Set, and not just because the needles are beautiful. The cable is one of the most flexible cables I have ever seen. I couldn't decide on tips, so I purchased out the Try it set which comes with two cables and three needle tips, one of each type of material.
I will admit that I already owned a convertible needles set, but this version is SO MUCH NICER, the needles are such a pleasure to knit with that I want to own all harmony wood needles!