These are contoured bases for crochet hooks, size I / J and D / E, providing better grip and stability. The holes measures 8.5mm and 5mm in diameter respectively, so the base of your hooks may vary. Use a dab of hot glue inside for additional hold.
Hot glue
a little bit of hot glue in the channel before inserting the needle will help with stability of your hooks are different sizes, or you prefer more needle sticking out.