here is a video about them
http://www.youtube.com/watch?v=TInsmUD-w0k
Quilters half square triangle square up laser cut acrylic ruler is what their website calls them
http://usaus.us/cart/index.php?main_...yword=bloc_loc
$22 for a 6" ruler is a little out of my price range, even if it is a nice ruler LOL