These are great! Use them anywhere you need a piece of cloth held down securely mooring, tonneau, & boat covers, dodger curtains.... The Shock Cord Cover Clip is installed by making a small hole in the fabric and snapping its self-locking sections together. Order Lacing Knob to complete the assembly. Acceptable size shock cord: 3/16" to 1/4" The height of the knob is 9/16" The OD is 11/16" (base) Recommended screw size is #8 x 1" Flat Head.