BuyJumpRopes Solid Core 4mm PVC Cord for Beginning Double Unders Kink resistant, 4mm diameter, solid core PVC cord. Generous 10 foot length. Sold individually and comes with free cord ends for easy sizing. Ultra durable, these cords can be used for jumping indoors or outdoor, on any surface! Use to build your own jump rope, or to replace worn out cords on you current jump rope. Excellent for athletes and Boxers beginning to work on double unders. Helps with establishing rhythm.