This block is a 9-patch with equal-sized segments, so normally you will find it only in sizes with an increment of 3 -- 12 inches, 9 inches, 6 inches, etc. See this explanation:
http://bethstrand.wordpress.com/2011...-2-churn-dash/
I did find the following tools that are supposed to allow you to design a block of any size using specialized rulers, but have never tried this myself:
http://www.multi-patch.com/html/churn_dash_pattern.html