For Sale: 25 Foot roll of 1/4 Inch Vinyl Sling Spline. This is used to repair outdoor patio sling furniture, Awning spline and also slide out covers on RVs.. The spline is designed to fit into the seam of fabric and then slid into a rail on a chair frame. Our vinyl, solid spline is extruded for outdoor use, it is commercial quality 100% virgin solid vinyl with ultra violet inhibitors manufactured into the product.