50' Vinyl 1/4" Outdoor Patio Spline, Replacement Awning Cord, Sling Chair If you do not have your old slings you may measure the slot width running up the rail and find which size you will need. Make sure you find the widest area of the rail slot and be sure your spline choice is just slightly bigger than that rail slot area so that it will keep the fabric in place when tightened For replacement purposes, you should measure the thickness of the original sling spline For Sale: 50 Foot roll of 1/4 Inch Vinyl Spline. This is used to repair awnings and outdoor patio sling furniture. The spline is designed to fit into the seam of fabric and then slid into a rail on a chair frame or awning. 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.