These are the AT version of the standard neoprene overboots (red). They are cut out for dynafit bindings (which worked well). I suspect they are a medium. My boots have a 300 BSL - about a size 9. These were used on one trip to Denali last year - no holes, no tears, no patches. Pick up a pair for this year's trip cheap. $75 plus shipping from Bozeman. Thanks