Didog Extra Long Lead Dog Leash for Training Tracking (Black,3 m/5 m/10 m/20 m) This check cord is made of strong, multifilament polypropylene nylon rope and boasts a solid brass snap. 3/8 Inch * 33 feet The product Obedience Check Cord is the top choice of many professional trainers to teach your dog to come on command and retrieve to your hand.