COATS&CLARK-Extra Strong & Upholstery Thread. Upholstery Nylon is a heavyweight 100% nylon thread for machine and hand sewing indoor and outdoor heavyweight fabrics. It is a bonded 3-ply nylon thread that is weather, abrasion, mildew and UV resistant. For best results use a size 18 needle and increase stitch length. This package contains one 150yd/137m snap spool of thread.