The Jackson Baby Hat by Allison calls for 1 skein of worsted weight yarn (pictured in Tosh Vintage).

Other beautiful worsted weight options include:
Rios
Far
220 Superwash Merino

Click here for even more worsted weight options. 

There are 5 sizes available (S 16" circumference as shown to XXL 24" circumference).

It's knit using size US 7 needles.