HurriClip hurricane safety clips are made of strong carbon steel. Simply slide the clips onto your plywood, typically 4 clips per sheet (depending on the size of your window), push the plywood into the window casing and you are DONE! Once the hurricane has passed, loosen the tension on the serrated part of the clip and pull the plywood sheet out of the window. Remove the clips, place in the provided bag and store until you need them again! How many HurriClip do I need? A average 4ft x 4ft window will need 2 clips on each vertical side spaced no more the 24” apart. For every additional 2 feet in height you will need to place another clip. Do HurriClip work on a inset less than 2.5”? No, HurriClip needs at least a 2.5” inset for them to grip properly. Do HurriClip work with my vinyl or Hardi siding? No, most siding products do not leave a proper inset for the clips to work. Does HurriClip work on sliding glass doors or large windows? Yes, however you will need to splice plywood together horizontally, and use 2x4 stiffeners horizontally across the span to reduce flex in your panels. How do I splice plywood for large windows? Use at least a 12” wide piece of plywood to place over the seam of your two pieces of plywood you are joining together. Use a combination of wood glue and screws to join the assembly together making sure the screws are started from the backside of your panel. What do you mean by a 2”x4” stiffener on end? This just means that the skinny side (1.5”) goes up against the plywood. Is there a maximum width that the plywood can span? No more than 8 feet, 2x4 stiffeners are recommended for spans any more than 4 feet wide. Will HurriClip scratch my brick, wood or stucco? There is a possibility that the clips will leave traces of scratching on any material.