Actually and easy star to do.  Looks complicated.  So if its a 12 in block:  The corners need to be 4 in.  Cut strips 2 /12 in.  That means you need a 4 in middle.  But you can't cut a 4 in sq.  One of those math phenomenoms: Directions say 4 7/8.  Me I cut them a little larger than 5 inches.  I have room to wiggle to trim to a perfect 4 1/2