Stayput Black Pull Cords for Shock Cords & Zippers used with Canvas Covers, 4 Pk Stayput Black Pull Cords for Shock Cords, Fasteners & Zippers often used with Canvas Covers, 4 Pack 4 Pack of Black Pull Cords Just use the Pull Cord to stretch the Shock Cord onto the Knob! Quick & Easy to Use! No more tired fingers from Snapping on Covers!