This knitting thimble is an extremely effective tool when you’re working with multiple colours since it helps you separate and guide the two strands. Just put the knitting thimble on the tip of your finger and thread each yarn through one of the two spirals.
If you’re using two strands, like you do in fair isle, this Prym knitting thimble is a great knitting aid. It helps you keep the two threads separated, and it can also help you keep an even tension.
It’s also a very popular crochet tool if you want to keep the yarn in check and achieve an even tension.