Thanks native texan and prism99. I'm using a size 12 needle. This particular piecing is the 3rd stage of this quilt and now that you've jogged my memory, there was some chain stitching previously that worked ok. Maybe I need to change my needle? Would that cause the thread to break? It's easy enough to try, so I'll do that. The tension is ok, both types of thread are no-name brands but they've both worked fine in the rest of the quilt.