Precision Piecing

 Here is how I make these bits into something. Shorten your stitch length a bit to 2.0 - 2.5 for a more secure stitch. I prefer to use 70/10 microtex sharp needle, but a 75/11 quilting needle works just as well. To set my sewing machine for success, I use a single stitch throat plat and a 1/4" foot.

 

Here's the test.  I used already cut 1 ½” squares of scraps.  Sew them together into a 9 patch block using a small diameter thread in the needle and the bobbin and then sew another block using fat thread in the needle and the bobbin.  Gently press the seams flat and measure.  It's obvious to see in my sample blocks that the blocks measure differently.

    

This sample above was sewn with a small diameter thread measures exactly the expected 3 ½" from cut edge to cut edge. 

The sample above was sewn with fat thread is shy the expected 3 ½" from cut edge to cut edge.