Stevie usually used Fender medium picks, and he played with the “fat” end. There are 17 verified variations of Stevie's custom picks, but he also used plain Fender picks, and freebies he picked up from guitar shops.
Two picks showing how Stevie used the fat end of the pick. Both have worn away at the top with his use.
Here's a selection of picks used by the man himself. For a detailed explanation of his picks, see Stevie's biographer Craig Hopkins' article here.