I use isocord thread. Have been using it for a couple years with no problems until lately. Last quilt broke threads really bad so i made a large piece of fabric with backing batting and used the fabric for top. i ran the machine fast and slow . made circles on fabric .It didn't miss a stitch or break a thread . sewed a beautiful stitch I have changed needle twice cleaned machine. It was serviced about three months ago. i also loosened the tension on the top thread.