Well, this depends on many factors. View or knitting needle and crochet hook size guide for working with popular yarn weights such as double knit, 4 ply, chunky & more.
Child's Temptation Poncho and Hat Kit - Blacker Yarns
Swedish-Influenced Raggsocks Pattern
Blacker yarns – louleigh
Ravelry: Arusha pattern by Verena Cohrs
Talland Tee - Project Kit - Blacker Yarns
Crochet Hook Sizes - Yarn Worx
combatting tight colorwork – Paper Tiger
blacker yarns — Diary — Melody Hoffmann
Crochet Hook or Knitting Needle Size Markers, Large Set , Sizes 0
blacker yarns — Diary — Melody Hoffmann
crafty Archives - Page 2 of 8 - Zeens and Roger
Crochet Hook Size Guide: Chart, Types & Comparisons for Beginners
How to Knit the Stockinette Stitch for Beginners - ChristaCoDesign
YARN REVIEW: MoYa Whisper — Emmy + LIEN