This extension plate is used to accurately space Twist-Lock Fasteners in an enclosure or roll-up panel when a window mullion is not the right width for your project. These extension plates are most commonly used in roll-up windows for a screened-in porch, but they are also seen in outdoor restaurant and café enclosures. Extension plates accommodate a window mullion width range of 1-1/4 to 2-3/4 inches. Install extension plates with wood screws (not included).