To do this cast on, you need a crochet hook the same size as the needles you will use to make your sock. Since I use a 2.5mm knitting needle, I also used a 2.5mm crochet hook to achieve this cast on. Good luck, and I hope this helps!
You can view the video here if the embed is down.
Let me know if you have any questions and I will answer them as quickly as possible!