Adult size S. These aren't the thin little bits of plastic that hover over your knee; these are serious braces. They offer protection against impact, side-to-side twisting, and hyperextension. Gently used; I'm only selling these because I got the Youth size, which fit me better. $100. They retail for $225.
http://www.motoworldracing.com/EVS-2006-Vision-Knee-Brace.html
(http://i25.tinypic.com/nmeypc.jpg)
(http://i32.tinypic.com/300b91y.jpg)