Memoi Spot on Basics cotton sweater tights are model SP-3405. These non-ribbed cotton tights are very economical. Great for school and to keep kids or ladies comfortable. Regarding sizing, they run a little bigger than some other brands. If a girl is just starting size 8-10 in Butterfly then she'd probably take a size 6 in the Memoi Spot on Basics. To get another idea of the sizing, I know that a girl/woman who is 5'4" and about 115 lbs. can fit comfortably into the size Average after they go into the dryer.