
It uses the zip tie idea (http://www.shapeoko.com/forum/viewtopic.php?f=11&t=412) along with the adjustable tension ideas in this thread (http://www.shapeoko.com/forum/viewtopic.php?f=11&t=426)
Basically use a dowel pin (or bolt or something cylindrical in shape) to wrap the belt around and and then tension using the tensioning block and two bolts. Pictures below will describe it better.