for regular piecing i generally use 10-12 stitches per inch- 16-18 for paper piecing (makes it easier to tear away the paper) and 4-7 for basting (makes it easier to remove them) i think alot of machines have a default setting at 2.5 which comes out to 10-12. i may lengthen it a bit if it's a heavy flannel- or tighten a bit if a home spun or fabric with a looser weave that is still thin.