Brands can change the gauge.
Originally uploaded by rchach
I am test running a bunch of Tunisian hooks side by side and the biggest thing that surprises me is the gauge results.
The yarn is all Cascade 220 Superwash, and the stitch pattern is the same. The hook size is all K/10.5 (6.5mm). The hook brands are all different.
The blue swatch is Crochet Master Plus, the pink Knitters Pride, the gray Denise. Amazing how different, each are at least 1/4" in width off from each other. Each are a different material, Denise is plastic, KP is wood, CMP is aluminum (with wood tip), and Tulip (not pictured) is bamboo. I have more to share with you soon (as soon as I can get through a few deadlines). Very interesting though so far.