I use Presencia 100% 60wt thread from Red Rock Threads online (can’t get it locally) for all my piecing. I like it as I can use a pretty small stitch length. I also frequently press open when it makes sense. Best thread I have tried yet. I buy the large cones and use a thread stand. When doing HST squares I cut the squares 1/4” to 1/2” larger. Mark 1/2 of squares on diagonal for stitching line with Sewline automatic pencils in lead color that works. Either one line & sew on either side or mark both stitching lines. Cut apart, using starch press seam open, then use Deb Tucker’s “Tucker Trimmer either 1, 2 or 3 depending on size needed and trim the squares down to the exact size you need. Turn out perfect HST’S every time.