So Fine Polyester Thread 3-ply 50wt 550yds50 wt. Designed for bobbin thread, quilting, and sewing. So Fine! is a lint-free, matte-finish, smooth 50 wt. 3 filament polyester thread. Due to its fine nature, So Fine! is an excellent blending thread and loved by both longarm and home machine quilters. So Fine! also makes a wonderful bobbin thread.