A head expander is used in replacement window applications where the replacement window is slightly shorter than the existing frame. The head expander can be insulated and covers the gap between the head of the window and the frame, making installation hassle free.
The sill angle is used in replacement applications where a window is being installed into an existing frame with a sloped sill to cover up the gap caused by the sloped angle. This is done to provide a clean finished look along the sill.
Sill angle with trimmable legs for easy installation.