Yarn Weights – One and Two Company Crochet Blog
Double Stranding 101 – Elizabeth Smith Knits
Using a different yarn for your pattern
Learn About Yarn Weights for Knitting - The Knit Picks Staff Knitting Blog
Yarn Weight Chart and Guide - Sarah Maker
The Best Yarns for Crochet Beginners (And the Worst Ones!)
Is it possible to convert flat double knitting into a circular
Yarn substitution at different weights — Jacqueline Cieslak
Which Yarn to use for knitting or crochet? – Jo-Creates
Determining Yarn Weights with Wraps Per Inch