when sewing your pieces for your block together do you use a single piece of thread or double?

Always single.

Single, if you use a double strand, or heavy/thick thread it will increase your seam allowances and throw off your block size. It's why most of us use a scant 1/4" to make up for the fabric you lose in pressing and the thread being in the seam line.

thank you so much. I am off to sew!!

single