BKrenning

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To turn a 10" block into a 12" block the chart shows to enlarge the pattern 120%. 10 x 1.20 = 12 so you would have to enlarge each template or measurement for each piece in a 10" block by 120% before seam allowances.

The Diamond Candy quilt mentioned relies on 4 basic 10" blocks to create a 20" block and it has sashing on the horizontal rows or so it appeared to me.

Hubby decided to go with me to Joann's which had me all confused so I didn't get a chance to look at the Double Pinwheel block you also mentioned. Here are some links to different blocks all called double pinwheel which is easily converted to almost any size since it is a 4 patch type block:
http://quilting.about.com/od/blockof...e_pinwheel.htm

http://tlc.howstuffworks.com/home/do...uilt-block.htm

The next one is the same as the last one only it "spins" the opposite direction: http://www.quilt-lovers-guide.com/do...ilt-block.html

http://www.mccallsquilting.com/qb/mc...101/index.html

My version of BlockBase has 3 more versions of the block--pictures attached below.