Coats & Clark-Extra Strong & Upholstery Thread. Upholstery Nylon is a 100% heavyweight nylon thread for machine and hand sewing heavyweight fabrics indoors and outdoors. It is a 3-ply nylon thread that is weather and abrasion resistant. For best results, use a size 18 needle and increase the stitch length. This package contains one 150 yard spool of snap thread. Available in a variety of colors - each sold separately. Imported.