I made the suggestion to a friend that they use a magic ring when designing their own items that are crocheted in the round. Since she didn't know how to do it, I offered to make a tutorial. I've never come across a pattern that I haven't been able to substitute a magic ring for chain stitch ring, but there may be some out there. So I suggest checking your gauge when you make the substitution. Any questions, comments or constructive criticism leave me a comment.
GNephew took the photographs for me so some of them aren't perfect.
7. Pull the tail to shrink the ring to the size needed. Here I've pulled it to completely close the hole. I do this for most hats that I make. You can leave it open part way if you choose. And then crochet! I continue crocheting over the tail until I have about 2 inches left. I weave that in opposite direction it was going to secure it.