This product is a Boye Flexible Cro-Hook, a type of double-ended crochet hook with a flexible cable connecting the two ends. This specific item is made by the brand Wrights in collaboration with Boye and has the model number 6214-G, with a size of 4.25mm A cro-hook is a special double-ended hook used for a technique called "cro-hooking," "cro-knitting," or "reversible Tunisian crochet". This technique allows for the creation of reversible, double-sided fabric, often using two different colors of yarn. The process is similar to Tunisian crochet but involves working with two hooks and two different balls of yarn, sliding the work from one end of the hook to the other.