European zippered Sham 20" x 30" $30
American buttoned Sham $35
Oxford Sham (photo way down below) $40
An Oxford sham has a flat edging all the way around and an envelope closure at the back.
An American sham is simply a long, unsecured bag: I so dislike the possibility that the insert will shift and show that I put buttons in the opening.
The basic sham is the plainest, with no edging, which means it is simply the exact size and shape of the insert, and a zipper closing.