This is a V shaped pulley design to be used with the XBlinds project. Its designed to drive the string you find on some window blinds. I use it on vertically hanging, horizontally open blinds. Only a little tension is required in the string for the pulley to drive it. I added the small 'teeth' because without it the pulley slipped too much. I made it 1mm thinner than the original pulley as I found the original pulley was just touching the front cover.