In 2009 I was in my local boot store and decided to buy two pair in the medium size. I loved them so much I bought ten more. At the time of the purchase I was a meatcutter who would make a five mile walk to and from work every day, this really sucked during the winter. These socks were just heavy enough to keep you warm and keep the sweat off your foot, but not as heavy as heavy wool socks as not to impede my work movement. In my mind they were the complete package. During the summer, going from 37degree cutting room to walking in three digit temps on my way home, these socks were amazing. My feet wouldn't sweat and get hot in the heat or cold, just complete bliss. Move forward to 2013 after wearing these socks all the time they were starting to wear out, creating around the top parts and losing elasticity. So I needed to buy some more. I could not find these socks in medium size any were so I contacted a sales rep and they said try the a578 and a66. I did it is two years later and although these socks are good they do not compare to the a504. Please make more of these in the medium size.