YLI, Aurifil, and Precensia all make wonderful hand quilting threads. But if these are not available to you, use any 40 wt. that is. To confuse matters, there's also #9 Perle Cotton that works nicely for the Big Stitch. The Big Stitch is a running stitch that is 1/4 inch on top and 1/8th inch on back (according to Billy Lauder in her book on Big Stitch).